Muchuu Ni Naruu Yo summary:

Towa and Yamato are twins with very different personalities. Yamato is loud, outgoing, and regularly gets into fights, and Towa is quiet, studious, and always suffering the after effects of Yamato's actions as he's always being mistaken for his brother.On his way home from school one day, Towa suddenly meets Mitsuru, a mysterious, young delinquent whilst being beaten up by the school gang who mistakes him for Yamato. But Mitsuru can tell them apart...