Omae no Koi wa Ore no Mono

Ishio and Mochizuki are sworn enemies, forever at war. One day, Ishio accidentally walks in on Mochizuki naked. When Mochizuki catches Ishio blushing, it gives him the perfect idea for revenge! He decides to wield his sexiness as a weapon, taunting Ishio for maximum public humiliation. At first the plan works… until Ishio starts pushing back! Soon Mochizuki finds Ishio pinning and kissing HIM against the wall instead of the other way around. Maybe flirting with the enemy wasn’t a good idea.
(Source: Tapas)
Includes side story: Tokubetsu na Asa no Hanashi