Katekyo Hitman Reborn! is a Japanese manga by Akira Amano. The story describes the life of a boy named Sawada, after he finds out he is next in line to become the boss of the most powerful mafia organization, the Vongola Family.
The doujinshi word describes two side characters, Yamamoto and Hibari, so if you want to see this two together, you can download it here~