Koisuru Idenshi

A short story about a pair of brothers who are also lovers. The older brother, Nen, plays in a live band and wants to eventually make his living as a guitarist. The younger brother, Satsuki, is happy in his relationship with his brother and has no hang-up about sex. One day, Satsuki is approached by the leader of the band, Akito, to "service" Akito in return for Nen to have a guitar solo in their Christmas concert...

(Source: Love For Pop Culture)