So I got the idea for this from a Tumblr post. I am not Uncle Rick and therefore do not own this content.

'Why won't you tell me?'

Nico scowled. He'd been so looking forward to having Hazel visit from Camp Jupiter over the winter break that he'd completely forgotten that she'd be asking him the same stupid question over and over again. When's your birthday?

'I told you,' he said, staring into his goblet. 'I don't want everyone to know. They'd just make some silly fuss. It would be totally embarrassing.'

'I wouldn't tell them, I promise,' Hazel wheedled. 'I just want to know. I'm your sister.'

'I haven't told Will either, and he's my boyfriend,' Nico gritted his teeth. 'He won't shut up about this either.'

The campers were having breakfast. Since Hazel was there, Nico was actually sitting at his own table for once rather than at the Apollo table with Will and his siblings. He loved her a lot, but she was really annoying him. He had to concentrate hard not to make zombies appear as a result of his bad mood.

'Look,' he said, looking her straight in her golden eyes. 'There's a good reason I can't tell you. Can you respect that?'

Hazel bit her lip. She knew what it was like to have a big secret that you couldn't tell anyone. She'd spent months at Camp Jupiter hiding the fact that she was meant to be dead. Still, she couldn't think why Nico didn't want to tell her his birthday. What harm would it do to tell her? Didn't he trust her?

She nodded.

'Sure thing.' She'd ask again some other time when he was in a better mood.

He gave a tiny nod of thanks.

They finished breakfast and went about their daily activities. Later that afternoon, Hazel grabbed Will and asked him about it.

'Yeah, he won't tell me,' Will shrugged. 'I figured he'd open up when we'd been dating for a few months, but no luck. He doesn't like talking about himself.'

'Don't I know it,' Hazel agreed.

'I'm just gonna give it time,' he said. 'I'm sure it'll come out eventually.'

A week passed. Hazel knew better than to bring up the subject again, since it was obviously a sensitive one. They had a nice week together, practising sword fighting, playing Capture-the-Flag, doing singalongs at the campfire (which Nico begrudgingly joined in because Will made him, although Hazel suspected he secretly loved it). He seemed to be in good spirits as they headed back to the Hades cabin together a couple of days before Hazel was due to return to Camp Jupiter. The bonfire had been particularly bright that night.

'Wasn't that fun?' she asked.

Nico grimaced.

'I feel a little queasy. I'm not sure if it's from those cheesy songs or having one too many s'mores.'

Hazel caught his eye and they both laughed. Nico did seem much more at ease…if she could just get him to trust her a little more…

'You…know you can tell me anything, right?'

Nico's face fell. He dropped his gaze to the floor.

'Yes.'

'Sooo…'

'I don't know, okay!'

Hazel blinked in surprise at this sudden outburst.

'Don't know what?'

'When my…when my birthday is. I don't remember. Now you know. Happy?'

'Oh…Nico…I had no idea.'

'Never mind. Just – forget I said anything.' Nico turned and disappeared into the darkness. Hazel called after him.

'Nico, wait! Come back, please! I didn't know!'

She chased after him, but he was gone. He must have shadow-travelled away.

Hazel went inside the cabin and sank down onto her bed. She felt like kicking herself. Of course. She was so stupid. How could it not have occurred to her that he didn't remember? He knew nothing of his old life. He hadn't even known who his own mother had been until their father had told him.

Their father…

A lightbulb seemed to click on in her brain. If anyone would know, Hades would. But no…that was a crazy idea. Right?

She paced around the dimly lit cabin, thinking hard, and stopped in front of the shrine to their father. Nico seemed pretty mad at her; she had to make it up to him somehow. She knew he visited the Underworld from time to time. Why couldn't she? She knew her way around, having been there for a very long time. It wasn't like she hadn't seen the place since being brought back to life. She'd had to relive her own death and judgment during her flashback with Frank. If she could do that, she could do this.

But how to get there? She was no good at shadow-travel. That was Nico's thing. She didn't want to attempt it and end up gods knew where. And she could hardly travel all the way to Los Angeles. That would take days, maybe weeks. She racked her brain. Wasn't there an entrance in Central Park? Yes – Nico had taken it with Percy one time. She'd ask Percy about it.

She got into bed feeling determined and mulled over the plan in her head for a few hours. Nico did not come back. Hazel assumed he'd gone to the Apollo cabin. Guilt weighed on her mind as she drifted into an uneasy sleep. She owed Nico for bringing her back to life. She had to make it up to him.

The next morning, Hazel's eyes shot open as she remembered her plan. She quickly dressed and went and knocked on the door of Cabin Three. A bleary-eyed Percy answered the door wearing blue PJ's, his black hair sticking up in all directions.

'Hazel?' He yawned and rubbed his sea-green eyes. 'I thought you were a Pegasus.'

'Um, what?'

'They have a habit of knocking on my door at ridiculous hours to ask for favours. Usually sea creatures trapped in nets.'

'Ooo-kay,' Hazel replied. Not wanting to get side-tracked, she asked:

'Listen, I need to ask you about the entrance to the Underworld in Central Park.'

Percy's brow furrowed.

'You're thinking of going to the Underworld?'

'Yes, to see my dad.'

Percy shuddered.

'Rather you than me. Why not ask Nico? He could take you.'

'No!' Hazel blurted a little too loudly, causing Percy to step back a little in surprise. 'I mean…Nico can't know about this. It's a secret. I just need you to tell me where the entrance is and how to get in there.'

'Well…I think it's called the Door of Orpheus. You know, the dude with the harp.'

'Lyre?'

'Yes, that. It's this big clump of boulders near to the pond. You have to charm it open with music, so I hope you're good at singing.'

'Hmm…' Hazel considered this. She wasn't terrible at singing, but she didn't fancy it in the middle of a crowded park. 'How did you open it?'

'My mate Grover played some music on his reed pipes.'

'The satyr?'

'That's the guy.'

Hazel had never met Grover, and she couldn't exactly ask Coach Hedge. He was at Piper's place, and anyhow, he'd probably just whack the boulders with his baseball bat while yelling 'DIE!' She'd have to get musical help from somewhere else – maybe Apollo's cabin. But she'd have to be careful of Will finding out.

'Thanks, Percy. You've been a massive help.'

'Hey, don't mention it. How are you getting to Central Park?'

Hazel grinned.

'Your favourite horse is taking me.'

'Arion?' Percy grimaced. 'You wouldn't like him so much if you could hear him cuss, Hazel.'

She laughed.

'Anyway, good luck with your dad. I hope things work out.'

'Yeah, me too. I'll see you around.'

Hazel headed to breakfast, so Nico and the others wouldn't think she'd vanished mysteriously in the night. Her brother was sitting at the Hades table when she arrived.

'Er – hi,' she said, sitting down next to him.

He nodded, not making eye contact.

'Listen, Nico, I…'

'It's okay.' Nico stared at his toast. 'Really. You couldn't have known. Just drop it.'

'Sure thing.' He seemed not to want to talk about it, which was fine with Hazel. She picked up her plate and headed to the bronze brazier, scraping part of her food into the flames and muttering 'Pluto'.

They ate the rest of the meal in silence. Things were very awkward, but at least Nico wasn't mad. She felt a fresh pang of guilt as she glanced over to the Apollo table. How much had Nico told them? Will must know that something had happened between them, and he didn't seem like the kind of guy Hazel wanted mad at her. He could probably break every bone in her body while naming them.

'So…what are you doing first today?' Nico made an effort to strike up a conversation.

'Oh, er…Pegasus riding.' Hazel deliberately picked an activity that she knew Nico hated, so he wouldn't want to go with her. He didn't like the Pegasi. Or rather, the Pegasi didn't like him. According to Percy, they thought he 'smelled like dead people' and refused to let him get on them.

As she expected, he turned his pale nose up at this.

'Right. I'm doing sword fighting. I'll catch you later, I guess.'

'Sure,' Hazel lied. They said an awkward goodbye and Hazel made like she was heading to the stables. Of course, as soon as Nico was out of sight, she changed her course.

She decided to check out the camp's supply of musical instruments. They were kept in a shed next to the weapons store. In the end, she settled for a ukulele. It was small, light, and she would definitely be able to make some sort of noise with it. The only thing left to do was call Arion.

As she headed up to Thalia's pine tree, she hoped the horse would actually turn up. Otherwise she'd have to borrow Blackjack, and she wasn't sure how she felt about flying. While her mind was on horses, she hoped Chiron wouldn't be mad at her for leaving camp without permission. Since she wasn't officially a resident of Camp Half-Blood, hopefully it would be okay.

She closed her eyes, concentrating hard.

Arion…I need you…

Within a few seconds, she felt a gust of wind on her face. She opened her golden eyes and beheld a majestic stallion.

'Arion!' She threw her arms round his neck. 'You came!'

The horse whinnied as if to say Of course I did, you silly girl! Hazel really wished she had Percy's power of speaking with horses. But maybe, as he said, it was best that she didn't.

'Okay,' she said, climbing onto his back. 'I need you to take me to Central Park.'

Without warning, the horse took off at breakneck speed, leaving a trail of dust behind him. Hazel's stomach flipped over – partly because of the sudden jolting take-off and partly because there was no going back now. She was on her way to the Underworld!

They raced through the strawberry fields, past farmhouses, and in no time were racing through New York City. Hazel felt that familiar feeling of being on top of the world – the wind blowing through her hair and snatching her breath away. Right now, she was unstoppable. She could do anything. Arion darted through streets and alleyways, past cars and pedestrians. Nobody noticed him go past, probably because he just appeared as a blur. Or maybe they thought he was just an extremely fast motorbike. They ground to a halt in Central Park and Hazel slid off.

'Thanks. Do you need some gold to eat?'

The horse neighed indignantly. Hazel interpreted it as Oh, please. That was barely a warm-up!

'Okay, suit yourself,' she laughed. 'Do you want to hang around here until I get back then?'

Arion neighed the affirmative and trotted off. Hazel sighed as she watched him go. It was time to find the boulders.

She spotted them about a hundred feet away and walked over, unslinging the ukulele from her back. Luckily, it was still quite early, about 9am, so there weren't many people around, just a few joggers and dog-walkers. She pressed her fingers against the strings and played a few chords.

At first, nothing happened. The boulders stayed stubbornly in place. Hazel glanced around, feeling a bit silly playing music to a bunch of rocks. Nobody was paying her any attention, however. She'd heard from Percy that New Yorkers were used to seeing people do strange things. She kept playing, and slowly but surely, the rocks started to move to reveal a triangular crevice.

She was hit instantly with that dark, damp Underworld smell that brought back her darkest memories. She shivered, starting to reconsider her mission. Did she really want to do this? I have to, for Nico, she told herself firmly. Before she could change her mind, she stepped inside and began to descend into the darkness.

The boulders slid shut once more, leaving her in pitch blackness. At least no unsuspecting mortals would accidentally be taking a trip to the Underworld. Luckily, due to her underground senses, she could tell where the steps were, or she would have plummeted straight down there herself.

After a couple of hours of wandering, however, she started to think that would have been preferable. Her feet were starting to ache, and she was getting tired. The stairs were fairly slippery, and Hazel wished they were a slide instead. That would certainly be more fun, faster, and not unmanageable with her powers…still, she didn't know which part of the Underworld she was going to emerge in. She didn't want to fall in one of the rivers and end up having her memory wiped or her body burned away. That would not be a very nice birthday present for Nico.

Eventually, however, she emerged out of a cliff face, with the River Styx rushing along to her right and the dark walls of her father's kingdom towering in the distance to her left. The next step was to get inside the gates. Nico said that he was usually able to get in without any trouble. Hazel wondered if it would be the same for her, as a daughter of Pluto. If not, she would just have to manipulate the Mist a little.

She took a deep breath and began to walk towards the ramparts of Erebos. She was shivering, although she wasn't sure if it was from cold or nerves. She could have sworn it hadn't been so cold last time. But then again, last time she had been dead. This time she was alive. Her living, breathing body did not belong in the Underworld.

She arrived at the EZ-DEATH line. The next problem would be the small issue of getting past Cerberus and the security ghouls. As she approached the giant three-headed Rottweiler, she thought back to a conversation she'd had with Annabeth. What was it Annabeth had used…a ball? A red rubber ball!

The dog was eyeing her and growling a little, as if sizing her up. He bent down and sniffed her with his middle head, and narrowed his eyes. Hazel had no idea if he'd worked out who she was, or if this would help her case at all, but she wasn't taking any risks. She snapped her fingers and the illusion of a red rubber ball appeared in her hand.

'Fetch!'

She lobbed the fake ball as far as possible in the direction that she'd come, towards the Styx. The dog gave an enthusiastic 'WOOF!', jumped right over her head and gave chase.

Everyone in the line screamed and panicked. The security ghouls went after Cerberus, trying to summon him back. In all the confusion, Hazel was able to slip unnoticed into the Fields of Asphodel.

This had been the part she'd been dreading the most. It had been her home for the best part of a century. Spirits chattered all around her. Poplar trees dotted the sparse black plains. Somewhere out there was her mother, Marie Levesque, who was here thanks to Hazel's pleading even though she had deserved Punishment. She tried to push this out of her mind and think of Nico, and Frank, and all her friends. They'd all saved the world together. They were heroes. She wouldn't end up back here.

She was both relieved and terrified to finally reach Hades' palace. Her heart was hammering in her chest. The Furies were circling the parapets. She hoped she wouldn't have to encounter them. She took a few nervous steps through the gates and into the garden.

Her eyes and senses were immediately drawn to the clusters of jewels on the trees - emeralds, rubies, and diamonds bigger than her fists. Her ability to sense precious metals and jewels was going into overdrive and making her a little dizzy. She stood gazing at them, open-mouthed, for about a minute, until a voice said:

'Hello?'

Hazel spun round and came face to face with a beautiful woman. She had long, silky black hair and chocolate-brown eyes.

'Who are you,' the woman asked, 'And why are you in my garden?'

My garden. Hazel realised the woman's dress had shifting patterns of all different kinds of flowers. This must be Persephone.

'You look very much alive to me. How did you get down here?'

Hazel took a deep breath. She'd faced all kinds of monsters and gods. She could do this. She could speak to her own stepmother.

'Lady Persephone,' she began, 'It's an honour to meet you. My name is Hazel Levesque, and I am a demigod. I am here to speak with my father Plu…er, Hades.'

The goddess's eyes narrowed. Her expression was unreadable.

'A demigod? I thought the di Angelo boy was the only one.'

'He was,' Hazel explained. 'He brought me back from the dead.'

'I see.'

There was an awkward silence, broken only by the screams of tortured souls in the distance. Hazel hadn't planned for this. She wasn't sure how her stepmother felt towards her husband's children. She just knew she had to make as good an impression as possible.

'My lady, if you could take me to my father, I'd very much appreciate it.'

Persephone studied her for a few moments.

'Is this important, Miss Levesque? The Lord of the Dead does not take kindly to being disturbed, you know.'

'Um, well…' Hazel bit her lip. How important was her question? This had seemed like such a good idea in the world above, but now that she was here, it seemed ridiculous. What had she been thinking?

She was, however, saved the trouble of answering. For at that moment, her father appeared on his throne.

'I'd say it's a little late for that.'

Hazel gulped. She assumed this was her father, for she'd only ever met him as Pluto, not Hades. He radiated power, so much more than she remembered from when they'd met before. She guessed it was because he was in his own domain. She felt drawn to him, and suddenly felt the urge to go and curl up at his feet and have a nice long nap.

'Um, hello, Father. Have I disturbed you?'

'You distracted Cerberus and caused chaos with my security ghouls. Did you think I would not notice that?'

'Ah. Yes. Sorry about that.'

'I assume this is important,' he said, 'Otherwise you would never have dared to come here?'

'Uhhh…' Hazel glanced to her side for Persephone, but the goddess had vanished. She was alone with her father.

'Just one question, Father. It's about Nico. We - we had an argument and I have to make it up to him.'

Hades arched an eyebrow. His expression was icy. When he didn't respond further, Hazel blurted at top speed:

'He doesn't remember when his birthday is and I thought you might know.'

Hades was silent for a long time. At least, it felt like a long time to Hazel. He pressed the tips of his skeletal fingers together and inhaled deeply.

'You would come all this way…' he said slowly, 'You would come down here and risk having to stay forever…to ask me that? You did not think to send a letter or an Iris-message?'

'Well…' Hazel felt her cheeks glowing warm. 'I also wanted to see you,' she admitted to the floor.

Suddenly she sensed her father's presence right in front of her. She looked up into his dark eyes.

'Hazel, it is not that I do not want to see you either. But I have chosen to ignore the fact that you were brought back to life, for your own sake and Nico's. This goes against my own laws. I cannot continue to do this if you present yourself before me. If we meet again, I will have no choice but to reclaim your soul. Do you understand?'

'Yes, Father.' Hazel studied his face with her golden eyes, remarking that they looked nothing alike. He was ghostly pale, with sleek jet-black hair. She was dark-skinned, with curly cinnamon-toast hair.

'Nico is lucky to have you as a sister. I would hate to have to change that. I know that you feel that you owe him a great debt, but this is not the way to go about settling it. I told him that my children rarely have happy endings, and that I would like for him to be an exception. The same applies to you.'

They gazed at each other for a few moments. Maybe, Hazel thought, just maybe, he wasn't the worst dad after all.

'It's January the 28th,' Hades said.

Hazel blinked in surprise. With all the things her father had just said to her, she'd almost forgotten the reason she'd come in the first place.

'Oh – thank you! I'll go now, and I won't bother you again.'

'That won't be necessary. I will send you back to camp. I can't have you distracting my dog again.' Hazel thought she detected the hint of a smile on his lips. She grinned despite herself.

'Goodbye, Father.' She took one last look at him before being engulfed by darkness.

Hazel appeared at the Hades table at Camp Half-Blood, opposite a very confused-looking Nico, who was halfway through his chicken nuggets. It must be lunchtime.

'What the…?' Nico stood up in surprise. 'Hazel? I've been looking for you all morning. Where have you been? Did you just shadow-travel?'

She hesitated, and then decided there was no point waiting to tell him the truth.

'I went to the Underworld to see Dad,' she confessed.

Nico looked at her blankly for a few moments, then gave a laugh of disbelief.

'Okay, very funny. Where did you really go?'

'I told you. I went to ask him when your birthday is. It's January 28th.'

Nico looked at her like she'd said she'd been to the moon.

'You did what now?'

She gave him a sheepish smile.

'I know it's hard to believe. But why else would I have this?' She unslung the ukulele from her back. 'I used it to charm open the Door of Orpheus.'

Nico's eyes softened.

'You would do that for me?'

'Of course. I literally owe you my life, Nico. It was the least I could do.'

Nico sat back down. Tears glistened in his eyes, but he blinked them back furiously.

'Was Dad mad at you?'

'Maybe a little,' Hazel admitted. 'He says I can't ever visit him again, what with the whole supposed-to-be-dead thing. But he also said…some nice stuff.' She didn't think it was the best idea to make Nico cry while they were in the pavilion with all the other campers.

'Hazel…I don't know what to say.'

'You don't have to say anything. Now you can decide whether you want to celebrate your birthday or not. It's completely up to you.'

Nico really wanted to hug her, but still wasn't very confident at that. He settled for an awkward hand-squeeze.

'Thanks.'

A few weeks later, Nico was shaken awake by his very excited-looking boyfriend.

'Rise and shine, Death Boy!'

He sat up in his coffin. (He really needed to get round to redecorating.)

'This had better not be totally embarrassing, Solace,' he warned.

'It won't be, I promise.' Will pecked him on the cheek and then brought out a present. 'Happy birthday!'

So it begins, Nico thought as he pulled back the bright yellow tissue paper. Will's cabin mates must have helped him out. Inside was a handsome watch. It was all black, except the number 12 was a tiny yellow sun.

'I made the sun as discreet as possible, otherwise I knew you'd never wear it,' Will explained, practically bouncing up and down with excitement. 'It's also a thermometer, so I can keep an eye on your temperature.' He grinned, tapping a small gauge on the side of the watch. Nico rolled his eyes but smiled.

'It's perfect. I love it.' He fastened it onto his wrist. 'And I'm glad you were joking about getting me the latest Mythomagic figures.'

'That's next year,' Will teased. This earned another eye-roll.

'I guess we'd better head to breakfast,' Nico said, both excited for and dreading the day ahead. 'I'll wake Hazel. She'll never forgive me if I don't.'

Hazel was visiting for the weekend. Nico had invited her over again; since she had gone to all the effort of finding out his birthday, she deserved to spend it with him.

He reached into her coffin and shook her awake.

'Morning,' she said brightly. 'Happy birthday!' She sprang out of bed and pulled a large, soft package from her dressing table. Nico opened it to reveal a new aviator's jacket.

'Since your old one got destroyed,' Hazel explained. Her brother made a small gesture towards her with his arms, then hesitated. She noticed and wrapped him up in a hug. When they broke apart, he looked awkward, but pleased. They turned to a grinning Will at the door and headed to the dining pavilion for breakfast.

As soon as they sat down, Hazel presented Nico with his birthday cards. She knew he wouldn't want to spend the whole day opening cards. She and Will had each given him one, and then she presented him with one big card signed by everyone: Percy, Annabeth, Jason, Piper, Frank, Reyna, Coach Hedge and Mellie, Grover, Tyson, Ella, Rachel, and Thalia. Nico blushed bright pink when he read it and mumbled something that sounded like 'you shouldn't have.'

The rest of the day was fairly normal. Because it was January, there were only a small handful of campers, which meant Will wouldn't be able to embarrass Nico too much. Mrs O'Leary showed up on the training grounds, tackled him to the ground and licked him from head to toe, making him laugh despite himself. At dinnertime, the nymphs brought him a small cupcake, with black icing and a candle. He blew it out and made a wish, glancing over to the Apollo table as he did so.

He knew something would happen at the campfire that night, especially since Will was in charge. He saw a mischievous gleam in his boyfriend's blue eyes as they lit the fire together. As anticipated, when they were done singing all the usual camp songs, Will made everyone sing Happy Birthday. Nico stared at the floor the whole time, his usually pale cheeks burning. He hated the attention, but seeing the looks on Hazel and Will's faces made it worth it. They looked so happy and pleased with themselves. He shook his head in exasperation. He loved his sister and boyfriend, even when they embarrassed him.

After he'd kissed Will goodnight and he and Hazel were getting ready for bed, he noticed a black envelope on his pillow that had not been there before. He opened it.

Nico.

Happy birthday, son.

I hope your sister and the Solace boy did not embarrass you too much.

Your present is in your pocket. I hope you like it.

Father.

Nico reached into the pocket of his new jacket and pulled out a tiny package that fitted in the palm of his hand. It was very small considering his father had once given him a zombie chauffeur, but he hadn't been expecting Hades to get him anything. He pulled back the black paper.

It was a ring. It was black, of course, with tiny engravements in silver. Looking very closely, Nico could make out pictures of his greatest achievements – fighting monsters, wielding the sceptre of Diocletian, shadow-travelling with the Athena Parthenos. He pressed a small button on the ring, and it projected ghostly, glowing images of the Underworld – his father's palace, Elysium, and the Isles of the Blest. Nico wasn't sure what to make of this gift, but it meant a lot that his father had thought of him. He kept the ring on.

'Thanks, Dad,' he muttered.

Perhaps birthdays didn't have to be the worst things in the world. He was glad he now knew when it was. He was glad to have a sister like Hazel.

Update: There is now a sequel - 'What's the Worst that Could Happen?'

'Nico attempts to throw a surprise birthday party for Hazel. Of course, things don't quite go the way he plans.'

Check it out if you enjoyed this story!