My Hyung's Omega

Do-yoon gets swept up in the heat cycle of Su-ah, whom he has cared for and loved since they were little, enough to believe he was his own younger sibling, and ends up in a relationship with him. Even though he is a beta, he wants to help Su- ah, who is suffering from heat, but this is the first time he has been crushed by an omega... Is this really a heat cycle? "I'll try harder because you like"