Yu-Gi-Oh! is by Kazuki Takahashi.
Domino City, despite the threats it went through, was still the metropolis people knew and loved. With its bustling streets, entertainment stops, and amusement park, it was still a place just to visit and hang out with friends. For one, however, it was a battleground.
Rushing through the streets was a boy seeming looking older for his age with purple eyes, spiky magenta and black hair with yellow bangs wearing a blue coat over a black shirt, gloves with a red and blue gemstone on the backs of them, on his hands, black jeans, and black shoes. Around his neck was a gold, upside down pyramid with an eye in the center hooked to a chain. Floating beside him was a young girl with white hair and skin and dark blue eyes dressed in a blue and white magician's uniform and holding a staff of the same colors.
They were running to corner a wolf with tea green fur looking rather feral. The two passed right through the people like they were ghosts while trying to corner it. When it lunged for a person having ice cream, the boy knew exactly what was coming.
"Protect those people!" he told her.
"Right," she said before using her staff to put up shields around the unknowing people. The wolf hit the barrier instead and was blasted back before growling at it. Hearing a whistle, the wolf chased the two down into an alley where no one else would get hurt from the scuffle.
"All right, no more running! It's time to fight!" the boy said.
The pyramid pendant around his neck glowed gold, and in a flash, the boy had seemingly aged to more of a teenage man. Extra strands of yellow hair had grown and the small yellow bang was gone. The clothes, however, remained the same, only there was a size change.
"Attack," the magician stated simply.
The man nodded before taking out a pendant with a brown crystal from his pocket. The crystal gained a brown aura around it before he tossed it into the air. The gems of the gloves glowed with a purple aura.
"Celtic Guardian!" the older male said. "Come forth!"
Catching the pendant, it burst into green light before the monster in question appeared by his side from it.
Mom and Dad, If you're reading this note, then I can no longer see or feel you anymore. You'll probably think I'm on a trip since I'm gone. But I'm actually right here. When I went down to greet you this morning, you didn't hear me. When I tried to touch you, I passed right through you. I didn't have time to be sad, though, because something attacked me while I tried to figure out what was going on. Now, I'm trying to reunite with my friends. I'm in someplace similar to your world, but different in that Duel Monsters, actual Duel Monsters (you know, the card game my friends and I play) are free to come here. A voice told me it wasn't always this way, though, and I was chosen to keep them from crossing over to your world along with others. I used to be Téa the schoolgirl. Now I am Téa Gardner, Warrior of Wind, fighting for my life against monsters that crossed over. See you when I get back from the Lanes Between. P.S. Why can't things be normal for a change?