From Exiled Rebels Scans:

Kirishima Naoto is handsome, hard-working and popular with his female co-workers, but has one major shortcoming: his extreme adoration towards his younger brother, Hokuto. Swearing off a proper romantic relationship for Hokuto's sake, Naoto frequently spends the evenings with his friend from college, Toudou. Though he knows that Toudou's gay, Naoto has never held it against him... Until one day, when he discovers that Toudou and Hokuto have been texting each other in secret and declares "If you promise not to touch my brother, I will take his place"!?