Kago no Naka no Serenade

Orphan Shion was picked up by a powerful company owner, Aihara Mutsuki, and put in a butler school for years. Upon graduation, Shion is brought to the main house and there, he met with Mutsuki's 5 sons. They were born from different mothers and are different in looks, age and personality. But all of them have become enchanted by Shion's beauty. Mutsuki asks Shion to choose one of them as his master....

[From Aarinfantasy Forums]