Shounen-ai, romantic love between boys, is a well-accepted genre within anime. However, most Shounen-ai anime simply present the romance without dealing with the implications that can arise from homosexuality.
Gravitation is unique in this sense: while the main characters explore emotional romance for members of the same sex, the actual question of its relevance to each character's personal sexuality is dealt with as well.
Gravitation is about a high-school student named Shindou Shuichi who longs to be a famous singer. He starts a band with his best friend Nakano Hiroshi and in classic high school romantic soap opera style, confusion abounds between these characters and others about who is falling in and out of love with whom. The romantic content in
Gravitation is specifically Shounen-ai, that is to say, it portrays emotional romance between boy characters but does not present any explicit sexual content. Sounen-ai, is in fact, popular in Japan among younger girls who find it sexually non-threatening. ~ Cammila Albertson, All Movie Guide