Harry Potter moves dimensions so often in so many crossovers, but not very much in this one. It's almost always Danny going to Harry's world. I wonder why?

Danny Phantom and Harry Potter aren't mine.

Enjoy!

Harry slammed the glass of lemonade back down on the table and sighed angrily when it splashed out and onto his arm. A quick twitch of his fingers made the hand clean again with a tiny magical pop, and the man stood from his table. Before it could be damaged, he hid his book away in the backpack on the chair next to him and swung it smoothly onto his shoulders. The backpack was a new creation, something suitable for the town he found himself in after jumping dimensions, and the wizard was pretty sure his old friend Hermione would be a little impressed if she saw it. Rune chains had been embroidered all over to add enchantments of protection against theft and durability, the shoulder straps had a quartz-anchored accio-lock that prevented anyone but himself from summoning it, and the largest interior compartment had space-expanding charms applied. Sure, he could only do the one area without destabilizing the entire object, and the expanded space wasn't as large as what Hermione had managed on her beaded bag, but one enhanced space was enough and the normal sized pockets were useful because they were normal.

An energy-charged ball of ectoplasm, carelessly thrown by one of the fighting ghosts in the horde above, came streaking straight for the two-month work of utility. Harry deflected it right back where it came from with a quick reflecting shield, cast with a simple twist of his wrist, and set his attention to the crowd of fleeing people. The black and white teenage ghost, the main protagonist who appeared in nearly every fight, had the hostile inhuman beings well in hand with his greater skill and Harry wasn't very concerned with them. A wave of his hand had calming charms washing through the mob. The effect was weak when so spread out, but it was enough to help people keep their heads about them as they ran down the street for cover, scattering quickly into buildings and down cross streets.

People were safe and the fight was already winding down, so Harry felt no need to stay. Until the yell and explosive crash in the brand new crater in the street, that is. The teenager rose up attacking, catching the new challenger by the leg, and slammed the vampiric ghost down in turn. He sank down into the street, vanishing from sight, and green eyes blinked in surprise when they met another not-glowing pair. Harry ignored him in favor of keeping an eye out for the real threat. Magic rushed down his right arm, the arm that now contained his wand after an incident in the Department of Mysteries, and he flexed his fingers, ready to defend himself.

Well, he would have been ready had the attack not come from directly beneath him. He flinched, hand only halfway through casting, when the fanged, grinning blue face rushed up and into him. The wizard went still, breathing deeply as ghostly power went flowing through his veins. It felt hot, but not burning hot, and the natural paths carved through his body by the magic he was born to channeled the foreign energy, restraining it. Beside his mind he felt the invader get confused, struggle a bit trying to possess him, then get furious. Harry couldn't help it, he started laughing. It was a rare thing when an enemy's plan backfired so hilariously.

"Plasmius!" The far-from-possessed man looked up to see the other ghost standing closer, fists and eyes both glowing bright green with power.

"So, this fool's name is Plasmius?" Harry cackled again, and the kid looked apprehensive. "I know you can hear me in there, so listen well." He took hold of Plasmius' own power, so conveniently handed to him, and sent it coursing to his hands just as if it were magic. They started glowing a rosy pink. "You're lucky I'm in a good mood, Plasmius. I could end you for this." He jerked inside, trying to escape. "Ah, not so fast. I don't want you causing more trouble." A glowing hand went transparent and Harry sank his own fingers through the skin of his chest and into the ethereal body of Plasmius. Then he pulled, carefully drawing the ghost back out but holding all the energy already set loose inside him. There was a tearing sound and the two separated completely. Harry wasn't sure how much of the ghostly power he had just stolen, just that he hadn't taken everything, or even half of everything, and that the ghost was clearly in pain. "I'll be keeping this," Harry's free hand flared brightly pink, "and I suggest you run while you have the chance." Harry set Plasmius free with a parting shove.

Red eyes glared. "You!"

"Me!" Harry mocked. He fired a bullet of the pink energy past Plasmius' head. More than pissed off, he jumped away into the air, hesitated, then flew away as he disappeared into thin air. "Good, it worked." Breath left his lungs in a woosh as Harry relaxed and let the new energy fade back through his skin.

"Who are you?" Right, the young ghost. Harry had actually forgotten he was there for a second. The scrawny glowing boy was clearly cautious, prepared if Harry suddenly turned on him, but the green no longer coated his fists.

"Hello. I'm Harry. Harry Black." He stuck out a hand.

"Danny Phantom." Danny looked down at the offered limb, uncertain after what he just saw, but shook it quickly once.

"Hah! I knew your name couldn't be Invis-o-Bill, that was just stupid." Danny groaned. "Ridiculous names aside, we should leave before those infernal news reporters show up. Bye!" The wizard ran, ducking into an alley and out of sight so he could safely apparate out. He did not see Danny Phantom chase after him, too late to catch him leaving.

The very next day, Harry Potter discovered his newly obtained power had settled in his chest like a second heart, right beside the flesh and blood one. It echoed his heart beat, sending the new energy through him as thin strands weaving among his magic. The feeling was ticklish and made him sneeze. The instant he did, he knew he had a problem because his arm vanished from the elbow down. That was only the beginning.

A week later, Harry knocked on the Fenton Family's front door and was led into the sitting room by a woman in a teal jumpsuit. "Hello Mrs. Fenton, thank you for seeing me."

"Please call me Maddie. You said you had a ghost problem?"

"A ghost problem!? You've come to the right place! Where is it!?" A very large, very orange man appeared in the doorway bristling with weapons.

"Not that kind of problem, er, Mr. Fenton. I was in a fight a week ago, and—"

"Who was it? Did Invis-o-bill appear?"

"Yes, but—"

"I'm gonna catch that ectoplasmic piece of—"

Maddie Fenton cut off her husband before he could get started on a good rant. "There's fresh fudge in the fridge, sweetie." The excitable man was gone as abruptly as he appeared. "Now, you said you were in a fight a week ago? And Invis-o-bill was there? Did he attack you?"

"No, not at all, he was busy protecting people."

"That ghost, protecting people?"

"Of course. He always does, when other ghosts attack. As far as I've seen anyway. But he's not important. I was attacked by Plasmius, the one with a cape and blue face."

"Plasmius? How do you know the ghost's name?"

"I didn't, Danny Phantom said it."

"Danny Phantom? You mean Invis-o-bill?"

"Danny Phantom is his real name, he told me himself."

"He told you his name?"

"Yes, he did, right after Plasmius attacked me, which brings me to my problem. Plasmius tried to possess me. When I resisted, he gave up and left, but I think I accidentally absorbed some of his power." Accidentally. Yeah, right.

"Really! Are you okay?"

"I feel fine, but weird things keep happening and I'm having trouble with it. Watch this." The strange tingling feeling had been bothering the wizard for nearly an hour by now, so he shivered it out and faded partially out of view. When he started sinking through the couch, he stood up. A loud sneeze restored him to normal. "See?" The woman stared at him, speechless. "Can you help me?"

"Yes, yes, of course. Come with me, I need to run a few tests first."

Harry was ushered to the basement, which was like an alien laboratory, and all manner of inexplicable tests began. Eventually she got around to trying to remove a small portion of the power, which was unsurprisingly painful.

"Stop stop stop stop! Ow... Let's not do that again."

"We can't remove the ectoplasm from you without pain..."

"That's fine, really, you don't have to remove it. If you can help me learn to at least keep it under control, it won't be a problem any more. You already checked to see it isn't harming me, and it isn't."

"Yes, it seems to have bonded with you well. A most interesting phenomenon."

"What happened, I heard yelling!" The orange man was back, filling the room.

Maddie filled him in, using words only Hermione had any hope of understanding. Their fascination with a human potentially sharing a ghost's ability quickly turned to exploring what Harry could do with those powers. Both scientists spent most of the afternoon trying to get the wizard to use ghostly abilities intentionally, with only limited success. Harry could shoot beams of energy—energy that had darkened to a purple-red over the last seven days—on command, but anything else he attempted was random. He would float, turn invisible, turn intangible, or start glowing faintly.

"Mom, I'm home!" A door slammed upstairs. Harry, trying to lift himself into the air, accidentally flinched and a rush to his head turned his hair white. Mr. Fenton was already up the stairs, but Maddie Fenton froze, just looking at his face. Harry rubbed his head vigorously, and the bird's nest returned to an inky black. A murmur of voices was followed by a loud "What!" from the arrival.

"Mr. Black, you said this morning that the Phantom was a good ghost?"

"Yeah, he helps people. He seems nice, though I only talked to him for a minute." What has the woman just realized that made her bring up the young ghost again out of the blue?

A boy, maybe fifteen years old or so, ran down into the basement followed by his father. Harry's presence, standing next to his mother, halted his steps at the bottom of the stairs. The expression of shocked recognition was a familiar one, and even though it was hidden quickly Harry saw it. He had been on the receiving end of looks like that since he was little, but this time there was no eye-flick to the forehead. How did a strange teen recognize him? "What are you doing down here?"

"It's amazing, Danny. Harry Black here has..." Bring on the technical terms. Everyone tuned the man out. Harry and Danny stared at each other and Maddie looked intently at her son.

"Daniel Jack Fenton, come here please."

Full name, said quietly. That wasn't the You're In Trouble voice, but it got everyone's attention. "Yeah, mom?"

"Tell me the truth, please. Are you..." She swallowed. "Are you Phantom? Danny Phantom?" He went absolutely still with heart-stopping fear, blue eyes wide and face deathly pale. "I think... I owe you a very big apology." She caught him in a hug, eyes flooding with tears. "You are. You are, how didn't I realize? And all the things we said, we did, we built and designed. I'm so sorry, Danny! I'm so so sorry! How could we, Jack?" Her voice dissolved into wordless sobs.

When the father joined the group hug thing, Harry decided to retreat upstairs. He was pacing around the couch when the front door opened again, letting in a red haired girl, probably an older sister considering how much she resembled her mother. "Who are you?"

"Harry Black. Here to visit the Fentons. Are you Danny's sister?" She nodded. "You might want to go to the basement. Family moment. Could you tell them I left? I'll just come back another time..."

"Sure." She gave him a mild look of suspicion as he walked around her and out the front door.

Harry went to the park, feeling a bit guilty.

Plasmius hunted him down the next day, itching for a fight. Harry sensed him coming and sidestepped the first blast of hot ectoplasm. Returning fire, he said, "Back for more? Bring it!"

The pier was evacuated swiftly as the two battled back and forth. Harry, unfamiliar with fighting ghosts and unable to fly, couldn't gain a big advantage. Plasmius, despite his many years of experience, did not know what he was fighting because the man used his stolen power only sparingly. Harry defended himself with quick spells, mostly shields, while trying to think of a plan. A heavy punch to the ribs sent him into the side of a building, and the ghost threw something metallic at him. The wizard wheezed, gathering magic to heal himself and reinforce the area.

The metallic thing exploded and a wire net wrapped around him as he fell to the ground. "What is this?"

"What are you?" Harry extended a single finger in reply. Plasmius hovered closer and pressed a button on a small remote in his hand. The net electrocuted him, weakly copying the effect of the cruciatus curse.

Harry, having suffered much worse on more than one occasion, bit down on his scream. He gasped when it was over and tried to reign in the ghostly energy that had been scattered wildly out of his control. It buzzed everywhere beneath his skin. His magic was a different story. "Is that all? Bzzt! Try again." Nodes all across the net sparked into uselessness as he destroyed its workings, then the net split apart, cut through cleanly with cutting curses.

With them so close together, Plasmius couldn't avoid the elemental casting of lightning. The follow-up blasting curse sent him soaring across the beach and into the lake with a tremendous splash. Danny Phantom landed beside him with an impressed whistle. "Wow. Never seen that before."

"Does that pain in the ass come here often? I've seen him a few times now." Aforementioned pain in the ass lifted himself, took one look at the pair of them, and left with a snarl.

"Yes, unfortunately. He's like me but older, and has the hots for my mom."

"He probably hates your dad and you, too, right?"

"Yeah, how did you know?"

"Knew a guy like him. One of my teachers. Took me forever to find out why he hated me so much."

"My parents like the guy. Well, they did." The ghost grinned broadly. "But since they know my secret now, I told them his too. By the way, they want to meet you again. But, uh..."

"What?"

"We had a long talk last night, and eventually we got to talking about you. You're the way my mom figured it out, you know? When she saw your hair turn white." Harry's hair wasn't white at that moment. "Anyway, she explained about trying to help you learn your powers and suggested I help you. Since, uhm, yeah." He gestured to his ghostly self.

"That would be great. All I can do is shoot things. Turning intangible is driving me nuts."

Danny laughed. "It was crazy when I first got my powers too. And trying to hide it!? I still don't know how my parents didn't notice. I broke so much glass. I wasn't allowed to do any practical work in chemistry, either."

A pause. "Back to your house?"

"Yeah." An armored van roared into view and screeched to a halt nearby. "There they are..." They watched the three other Fenton family members pile out of the vehicle. Harry gazed at the mobile monstrosity.

"Danny?"

"Yeah?"

"What exactly is on the roof of your house?"

Yep. May or may not be a one-shot. Please review!