Yu☆Gi☆Oh!

Yuugi is a somewhat frail young boy who happens to be a big fan of gaming of any kind. But when he solves an ancient egyptian puzzle he is granted all the powers of darkness. Now when confronted with danger and injustice, he transforms into a much darker and dangerous form, and proceeds to dish out the justice and punishment for those who so richly deserve it. (Source: AnimeNfo)

Cardfight Vanguard

The protagonist of this story, Sendo Aichi, is a timid boy in his third year of middle school. He had been living his life looking backward rather than forward, trying not to stand out. However, he had one thing that kept him going - the "Blaster Blade," a card from a card game that was given to him when he was little. That card is the reason why he begins to engage in Card Fights, something that changes his life drastically. The name of the card game is "Vanguard." The game takes place in a different planet called "Cray," and due to a never before seen play system, it becomes popular throughout the world. Aichi, immediately attracted by Vanguard, meets friends such as Tokura Misaki and Katsuragi Kamui, along with other rivals. Through friendly rivalry with them, Aichi begins to enjoy a fulfilling life. Aichi, however, has a goal: to once again battle with a Vanguard Fighter by the name of Kai Toshiki. Kai Toshiki is an aloof and cold-hearted high schooler who has outstanding abilities in the world of Vanguard. He is also the reason why Aichi started playing the game. For him, Toshiki is the person who saved him from his boring life and introduced him to Vanguard. In order to get better at Vanguard, Aichi puts his soul into it every day. He wishes that someday, he'll be able to battle Toshiki and have him recognize his worth. (Source: Crunchyroll)