GAWD I'M SLEEPY RIGHT NOW!

Nice long chapter for you guys this time!

Just a very quick Author's Note; the 'signature scenting' with OP and Tess in this chapter is something that only came to mind WHILE I was writing it hahaha.

Please bear in mind that it is NOT Sparkbonding, it has NOTHING TO DO with it at all, it's simply the bearing of a genetic signature; a smell so to speak.

Again, SimpleRhapsody has inspired me with her awesomeness; I used her idea of forehead contact being a Cybertronian gesture. While it doesn't mean quite the same thing that it does in her fic, I still got the basic prompt from her; so I HOPE YOU DON'T MIND! If you do, I will quite happily change it!

Anyhow, Reviews are loved; as always.

ENJOY!

"Are you ill?" Ratchet asked conversationally, waving a wrench in her general direction as he spoke.

Tessa looked up at him with a confused expression, "No…why; do I look sick?"

The vibrant yellow medic bot shook his head in response before he spoke again, "Not particularly. You just seem…unusually quiet today; is there something wrong with learning how to wire an Energon gun?" his tone was relatively serious, but she could hear the underlying concern in his voice; he was trying to make sure she was alright without lowering his gruff and professional exterior. She gave a smile at his adverse humour and looked up at him.

"No, of course not; It's just…my brother went back to work yesterday. He's a truck driver, so I don't get to see him often when he goes out on the road."

Ratchet was silent for a moment, "…He was the one that stayed in your home; correct?"

Tess nodded in response; picking up a piece of wire in her section of the cannon before shrugging vaguely, "Yeah. I guess I just miss him when he goes; we're a close family."

There was a moment of dim quiet as her voice trailed off; the two of them working on the firearm (one of Mudflap's basic weapons) before she heard Ratchet clear his vocal processor awkwardly.

"I thought about you research for the temperature weapon; while you and Optimus were gone…" he said conversationally; hoping to distract her from her misery. This got her attention, and suddenly she looked up at him with a bewildered and curious expression.

"Really? What about it?"

"You won't be able to create any sort of valid prototype unless you perform some controlled tests on reactive subjects." She looked a little bit confused, so he decided to explain it in a little more detail, "If you're going to try and create a weapon that will either kill or handicap a Decepticon; you will first need to test it to see if it actually works on them. I was thinking about this while you were away, and I've decided that the next time we hunt Decepticons; I'm bringing you back some samples."

"…Samples?" she echoed, "You mean like…body parts? But if they're not alive…how do I test them?"

Ratchet found her naivety amusing. For all her ingeniousness with mechanics and fusion engineering; she still knew so little of how their species functioned. "The body parts of a Decepticon are still reactive after they have been amputated; still living, in a sense. A similar process, I suppose, to an earth spider. The detached limb of a Decepticon will still react to heat or cold if we expose it to them. I will make sure to try and secure some samples for you the next time we have a mission. Perhaps you and I can run some controlled tests on them then."

Tessa suddenly gave a laugh and shook her head in disbelief. "This is hilarious!" she exclaimed, "Most people bring back a t-shirt as their souvenirs, but you Ratchet…" she paused to laugh again before continuing, "…you bring back body parts."

He shrugged nonchalantly, clearly not bothered by his own apparent, cold-blooded attitude; after all, this was in the name of science. What had to be done, simply had to be done; and that was the matter of it. "If you don't want me to…" he said seriously, an underlying cheeky tone lacing his voice; Tessa scoffed and picked up a bolt that was strewn on the table before throwing it at him playfully.

It hit him in the chest before bouncing off and rolling away somewhere, "Oh don't you even, Ratch! I appreciate the gesture; it would be an incredible help, thank you." She smiled up at him before stretching her arms high above her head and arching her back; feeling her spine crack in several places as she unbent herself, "I'm gonna take five and go get some Skittles. I'll be back soon to help you finish, okay?"

Having already delved back into his work, the medic nonchalantly waved her away as somebody would a small, pestering child. She smiled at the motion and jumped down from her chair; heading towards the barracks hangar so that she could get the Skittles from her locker.

She enjoyed working with Ratchet; it wasn't very often in her life where she'd had somebody who knew more about machines than she did, someone who could teach her. Despite his seemingly indifferent and professional demeanour, she knew that his heart -or Spark- was in the right place and that he genuinely cared about his comrades. She pinned it down to the fact that as a medical officer, he had probably watched a lot of teammates die in the war; and because of that it didn't pay to get too personally involved with others.

It was sad in a way; and she felt for him, she really did. But either way he still had people that were important to him; and she liked to think that she was one of them, at least in a small way.

Stepping out of the hangar and into the glaring midday sun, she felt an overwhelming sense of gratitude that she'd dressed in her work shorts and a tank top; given that it was incredibly hot weather. She hated summer…with a passion! Especially when it was humid, because it would make her hair stick to her and her clothes would get annoyingly uncomfortable.

As she reached the barracks and headed into the locker room, she wiped her hand across the back of her forehead and exhaled heavily; relieved for the air-conditioning in the locker room.

Twisting her combination into the dial, she pulled open her assigned locker and picked up a fresh bag of her fruit lollies from the shelf, tearing a small corner and dropping some into her palm. Tipping her head back, she tossed them into her mouth and chewed happily before rolling the packet and stuffing it into her pocket.

It was two days since her father's birthday gathering; she had taken the Monday off considering that she hadn't gotten to bed until very late the Sunday night. Optimus, true to his word, had maintained the Holoform until she fell asleep in his arms; but she had woken up on her own. When she had questioned him about this, he'd explained that given his own lack of energy from exerting the Holoform for an entire day, it had flickered a short time after she'd fallen asleep and he'd been forced to let it dissipate. When she'd woken up and exited her room, she'd found he had already reactivated it from the truck and was conversing with her mother; who had resumed her favourite activity of gushing proudly over her daughter.

It was Tuesday now, the first day that she'd been back at work since their weekend together, and she'd spent the entire day in Ratchet's company; having wanted to bounce some prototype and research ideas off of the medic.

As she pondered her thoughts, she heard an engine approaching and turned to see the sleek, silver Corvette approaching her; rolling to a stop beside her as she walked slowly across the tarmac.

"Hey, Swipe." Tess said, smiling affectionately at the sports car, "What's up?"

The sound of hydraulics was heard as he changed into his bipedal form and crouched beside her with as close to a grin as his metallic matter would allow.

"Not a lot," he replied jovially, leaning his face in close to look at her, "Just wanted to say hello."

Tessa scoffed at him and shook her head with an amused smile and pointed at him, "Liar," she accused with a smirk, "you just want details about the weekend." She playfully pressed her palm to the plates on his face and pretended to push him; obviously unable to do so due to the size and weight difference.

He laughed and mockingly raised his hands in surrender; her own palm still pressed to the space that acted as the bridge of his nose. "Alright, alright I confess; I'm absolutely just-"

All of a sudden, Sideswipe completely paused his words, appearing confused about something. Tessa looked up at him in concern.

"Sides? Are you okay; wh-what's wrong?" she asked worriedly, cocking her head to the side.

The Corvette bot inhaled deeply, his expression still perplexed. That was one of the things that still amazed Tess about the Autobots; the fact that despite being made of metal, their faces had just as much animation as any human.

"Sideswipe-?" she repeated before he cut her off.

"-No, nothing is wrong," he said quickly, "It's not that; there's just…" furrowing the metal of his brow as his blue optics focused on the hand that was pressed to his face. He raised his left arm and carefully held her forearm between his massive thumb and forefinger; sniffing the air intently before he spoke again, "You… it's only faint, but…you smell of Optimus."

Tessa made a choking noise and withdrew her hand, looking at it as though she had been bitten by something.

"I…do?" She tentatively raised the arm to her face and pressed her nose to her skin; inhaling deeply, "But…I don't smell anything!" she exclaimed confusedly.

To this, Sideswipe shook his head, his elbows rested on his knees as he looked her in the eye.

"Of course you don't; humans can't pick up on our Energon signatures. Tell me, all personal curiosity aside; did you interface with Optimus' Holoform?"

She flashed scarlet, but shook her head furiously, "No! No we didn't."

"But you touched the Holoform, yes? Human contact; correct?"

"W-well of course I did. We kissed and he held me, I was touching the Holoform constantly; why? What's this about?"

Sideswipe appeared perplexed, but seemed a little more at ease now that he had located the source of the scent. "Every Transformer, whether they're an Autobot or a Decepticon, has a unique Energon signature; a scent that we can detect. Being soldiers, we've learned to guard our signals against Decepticons so that they can't locate us; but we can still detect our allies. It's complicated, the closest thing I suppose for you to compare it to is…um…"

"Like radar?" she offered, "With like…hostiles and friendlies?"

"Yeah! Exactly!"

She looked at her hand once more, turning it over to view each side with a confused expression, "But…I still don't understand what that has to do with me?"

Sideswipe rolled his eyes in a mockingly exasperated tone before deciding he would have to explain; she was like a little Sparkling sometimes.

"Because you've been in near constant contact with Optimus' Holoform all weekend, in what I'm guessing were probably a few minor compromising ways; am I right?" She flushed scarlet, but didn't deny it, "Exactly, anyway; because of that some of his Energon signature has applied itself to to. I can detect it; in fact I'm surprised Ratchet hasn't said anything, haven't you been with him all morning?"

"Well…yeah… Wait! But, what I don't get is…" she pressed a finger to her temple as she contemplated her words, trying to wrap her head around the concept, "I've been in constant contact with the real Optimus for…for months. Why wouldn't you have…smelt something before now?"

Sideswipe shook his head, "In our bipedal forms, the signature transfers usually occur on the face; and it's much stronger than what you've got on you. A Holoform's Energon signature is weaker; kind of like trying to rub perfume on someone through a glove. It's the same scent…just a lot weaker. But the transfer usually only happens in the case of a mate; or in yours and Optimus' case, a potential mate. But it's usually subconscious…a Transformer can't converge their signature unless the Spark knows it will be willingly received. Did anything…romantically important happen between the two of you?"

Tess visibly fidgeted now, but she wanted answers; so she answered his question despite her embarrassment at the situation.

"Well…we kissed? Uh…oh! There was a moment with the Holoform when he showed me the scar on his chest, where Mega-" she stopped and choked on her own words, hating to have to say that thing's name; despite her having no idea who he was or what he looked like. All she knew was that he had taken her Optimus away from her once already, and she hated him for it, "where Megatron stabbed him through the Spark…Would that have changed anything with Chief's Energon signature?"

Pondering for a moment, Sideswipe shook his head, "No. It's emotional, I'll give it that…but it's not enough for his Spark to have noted you as willing to receive the scent… What could've…" he trailed off into his own curious pondering before the answer hit Tessa like a ten-tonne Transformer.

"Wait! I think I know what it might be…" she felt herself smile at the memory; her eyes growing distance as she recalled the conversation they'd had by the fire, "I…I told him that I loved him."

A whirring noise came from Sideswipe's form as he shifted rapidly to look at her, "You did; really? What did he say?"

She looked at him curiously, "He said that he loved me; why? Does it really matter what he said?"

"Of course it does!" he insisted, sounding deadly serious for once, "For a Cybertronian to actually confess love on a romantic level is…well, it's not exactly something to take lightly. Our race feels much more deeply and eternally than yours; and a confession like that has a massive amount of magnitude to it. Especially coming from Optimus…He's never been one to let others in on a personal level very often, it's a dangerous thing to do when everyone around you has the capability of being offlined."

Tessa gave a soft smile and crossed her arms around herself, her heart swelling lovingly just thinking about how much he meant to her, "I know that. I know what you mean by it…not letting people close, especially during a war like yours…it just sets you up for heartbreak when you lose someone." She looked up at Sideswipe and placed a hand on his leg, giving him a serious and loving look, "But I'm not in the centre of this war; I just stand on the sidelines. Even if I were in direct danger because of it, do you really think that I would trade my chance to have met him for the opportunity to be safe again? I wouldn't consider it, Sideswipe; not for a second."

To her surprise, he chuckled; clearly amused by her dead serious tone, "I know you wouldn't. That's what makes you special to him, Tess. You know exactly what you're running into; but you still won't turn around and get out while you can." He noticed that her shoulders squared a little, seemingly defensive; but not in an aggressive manner.

"I won't be the weak link," She said, and he noticed that her tone seemed a little darker this time; like she'd said this to herself before, "and I will never run away."

Shaking her head at herself as if to try and clear the darker air their conversation had taken, she looked back up at him with her usual expression; the corners of her lip turned up to give her face an open and friendly look, something she always seemed to have.

"So since I haven't seen Optimus in his actual robot form since the weekend…does that mean that next time I'm around him, his signature will rub off on me?"

Sideswipe shrugged vaguely, "More than likely; but the pheromones are emitted from our faces, particularly cheeks and foreheads. You'd probably find it's stronger in the areas where his Cybertronian is written; given that it's an important part of him."

"Good to know, thanks for the information, Sideswipe!" she exclaimed, backing away and looking for the Autobot hangar.

"No problem. H-hey! Where are you going?" he called, seeing that she'd turned in the direction of their hangar. She whirled around without stopping; she had a huge grin on her face that just screamed that she was up to something.

"Do me a favour and tell Ratchet that something came up and I'll be a little late!" she called out to him, "Optimus has some…paperwork that he needs to sign!" then she spun back on her heel and kept running towards her destination.

Sideswipe took a few seconds to get the joke, and then he had to chuckle to himself, "Energon signature…cute pun, Tess," he shook his head with another amused laugh and headed for the medical bay where Ratchet would be, "You sure know how to pick 'em Optimus Prime…"

-0-0-0-0-0-

When Tessa had reached the hangar and opened the door; she was both relieved and disappointed to find that Optimus was the only Autobot there. Jolt and Arcee had been taken out for a training exercise with Ironhide earlier that morning, and Sideswipe had apparently been racing with the twins before he'd left to talk to Tess; so Optimus had evidently taken the time to get some recharge from the weekend; it had been tiring for both of them.

As much as she had wanted to see everyone, her mission right now meant that it was probably better that it was just the Prime. He was currently in his Peterbilt form, and given that he made no motion to greet her as she stood before it; she realized that he was in stasis. She felt a little guilty for having come in whilst he was resting, but with Sideswipe's new information tossing itself back and forth in her brain; she didn't want to put this off.

Tess wanted his Energon signature to be recognizable to every Autobot on base.

A gentle, teasing smile came to her features when she decided to play with him a little; to relax him. He got so little chance among his soldiers to lower his guard, and she wanted to offer him the opportunity with her; he didn't have to hide anything in her presence.

Stepping forward, she gently touched her fingertips to the grill of the truck, tracing the chrome tenderly with a soft smile. "Chief…" she whispered airily.

No response.

Keeping the pads of her fingers touching the metal, she walked around to the driver's side of the truck; trailing her hand along the truck with a loving, feather-light touch, "Optimus Prime," she sang quietly, stopping at the driver's side door and thrumming her fingers on the smoke stack. She planted a kiss to the chrome metalwork before hearing a deep rumble from within the heart of the truck; similar to the sound Aaron would make when she had to wake him up early, "Wakey, wakey…" she hummed as she traced her nose over the chrome smoke stack.

"…Tessa…?" he murmured softly, his voice sounding distant as he came to.

"That's my boy…" she shushed soothingly, almost purring at him with pure affection, "I hate to wake you up, Chief…but there's something I need you to do for me."

"Anything."

She paused for a minute, drumming her fingers lightly on his paintwork before she smiled and backed up a little, "Can you transform? I need you to be bipedal for this…"

Despite his tiredness, he agreed; truth be known he was curious to see what she was up to. He shifted into his true form a little slower than usual given his need for stasis; and when he had he realized that Tessa was no longer standing where she was before. He scanned the floor of the hanger almost worriedly. "Tess?" he called.

"Up here, Optimus." Came her voice from behind him. He turned and found her on the walkway; to be closer to eye level with him; he approached slowly and placed a hand on the railing.

"What is it that you need me to do…?" he asked gently.

Tessa bit her bottom lip for a moment, suddenly feeling bad for waking him now that she could see just how much his exhaustion had caught up with him; but since he was awake now she decided to get it over with so that he could go back to sleep.

"Lean in to me," she said gently, "your face; bring it close."

Her answer confused him, but he chose not to ask her why; he would just see what she planned to do. Obediently he craned over the railing and leaned in very close to her, his neon blue optics burning intensely, cheekily, into her eyes. "Is this…close enough?" he rumbled.

Tessa, who felt a chill run up her spine just hearing his voice so close, knew her cheeks would be burning right now, but she didn't really care. Her blush did not embarrass her anymore; because Optimus gave her nothing to be embarrassed about. Taking a step forward, she raised a hand to touch the vents on his cheek, exhaling a little nervously at what she was about to try and do.

"Close your eyes…" she whispered gently; not wanting to break the quiet atmosphere of the hangar, "trust me."

He obeyed.

She watched his optics shutter closed before she returned her attention to his face. Tracing her hand down the vents of his cheek, she ran her fingertips tenderly over his lips; feeling him press a kiss against her hand as he felt it there. This made her giggle and thrum her fingers scoldingly on his top lip.

"Stop that, you tease," she murmured, serving him a 'punishment' by pressing her own lips to his mouth and planting a kiss there. She was surprised to hear a chuckle rumble from his vocal processor.

"Me?" he asked innocently, not opening his optics at all, "I believe you are the one doing the teasing. But by all means…continue."

She smirked to herself, glad that he couldn't see her as she finally settled her hands on the blue plating of his cheeks; running the pads of her fingers over the Cybertronian grooves in the metal. Taking in a bracing breath, she pressed herself against the cold metal surface, causing the Prime to open his optics out of curiosity. She held herself to the plating, her cheek pressed against him firmly. Optimus couldn't take the suspense anymore.

"Tess," he chuckled endearingly, "what exactly are you trying to do?"

"Sideswipe told me about Energon signatures; he smelt the Holoform on me. He said that me telling you that I loved you, and vice versa, probably triggered your Spark trying to…I don't know… 'mark' me I guess."

He paused for a second before responding, "…He did…? But…what does that have to do with…this?"

"He said the Holoform's signature, even though it's still yours, isn't as strong as the one the real you would give off…" she said, backing up a little and holding her hand to his face. Optimus shot her an understanding, but confused expression as he regarded her before him.

"That is true, but that still doesn't explain why you are doing what you're doing." He smiled.

Tess looked him in the eye seriously; her expression leaving very little room for debate, "I'm trying to steal your Energon signature you oblivious old robot. I want you to mark me with it."

His optics opened a visible amount wider at her words, before understanding shot through him, "Oh…" his metal lips were unable to hide a touched and joyous smile as he reached a hand up over the railing and laid it flat for her, "then let me show you how to accomplish it properly, my naïve young human."

Once she was safely cupped in his hand, he stood to his full height and brought her close to his face; lifting his free hand to tenderly touch her hair, stroking down the entire length of her side. Then he raised her close to him and lowered his voice to a rumble as he spoke to her, "Your forehead," he murmured, "touch your forehead to the bridge of my nose. Hold it there firmly and do not move."

Tessa did as she was told, not closing her eyes as he held her there. To her surprise, he raised his free hand and cupped it over his face as he shuttered out his optics; effectively trapping her in relative darkness, which made her squeak in worry.

"It's alright…" his voice rumbled gently, echoing in the cupping of his hand as he repeated her phrase from earlier, "trust me."

There was a few seconds of complete silence before Tessa heard a strange buzzing noise; almost a crackling. Then she noticed a blue light filling the dark cavern of Optimus' palm from below her, and as she glanced down between the gap between his face and the hand she stood on she saw something extraordinary. The markings on his facial plates were glowing blue with Energon; filling them and making them crystal clear. After a few seconds the Energon began to seep out of them before casting thin, glowing blue lines up his face towards where they were joined. She gasped in surprise as a tiny electric zap shocked her forehead, but obediently she stayed put; noticing that almost immediately the blue energy began to subside and fade.

Finally, Optimus withdrew his hand and let in the light; opening his optics to look at her gently. "All done," he said softly, "you now bear my Energon signature…my scent if you will."

Withdrawing her forehead from the bridge of his nose, she felt breathless from the experience; having to take a few seconds before she spoke, "…But…Sideswipe said that the signature marking is subconscious; that Cybertronians don't have to actually do the marking…?"

Optimus shook his head gently in response, "While that is true for other Transformers, both Decepticon and Autobot alike, I am a Prime. For me to mark subconsciously would be far to random and dangerous to risk; a Prime must choose who bears their Energon signature. In the Holoform it is automatic, just like any other Cybertronian; but for my true form it must be given consciously as I have just done for you."

Tess felt a little lightheaded from the magnitude of the situation, and she placed a hand on the tip of Optimus' nose for support before she planted a kiss there, "Well then…" she whispered, "I'm honoured that you chose me to bear your signature…" A chuckle beneath her caught her attention, and she realized that he had a slightly wistful tone; as if he were talking more to himself than to her.

"Oh Tessa…" he murmured in a soft, teasing voice, shuttering his optics again and nuzzling her tenderly in their close proximity, "My Tessa…it was always meant to be you…"

A fierce blush flared across her cheeks at the confession, rubbing her fingers affectionately on the metal of his face before she gave a soft, breathless giggle, "I love you, Chief."

"My Tessa…" he purred distractedly, clearly reeling in some kind of afterglow.

Maybe it affects them more than it does for me? She thought, I am only human after all; I don't feel what a Cybertronian would feel

"Optimus," she murmured a little more firmly than before, causing him to open his optics and look at her, "I have to finish helping Ratchet in the med bay; any chance you'll be letting me down any time soon?"

He offered her a rather sheepish smile before he leaned forward, planting an awkwardly cumbersome kiss on her head before gently lowering her to the hangar floor, "You're right," he said quietly, "I should probably go back to stasis, in any case; but I am glad that you woke me for this…

She pressed a hand to his cheek with a smile before she walked backwards toward the edge of the hangar; the two of them maintaining firm eye-to-optic contact until she reached the door and grinned at him embarrassedly, "Sleep well, Chief; I'll see you later."

"Most absolutely," he said gently before morphing slowly back into the Peterbilt; the noise ringing through the hangar in its familiar way. Tessa watched fondly as the truck rolled into the space it had been parked before she'd intruded and giggled to herself at the thought of what they had just accomplished.

Then she gently shut the door to the hangar behind her and left him to get some well deserved rest.