From Renta! 665q4j

Kaoru, a high school student infamously known as a fighting-fanatic, gains a sudden fascination with a new transfer student who is rumored to be incredibly dangerous. One day, he witnesses this mysterious underclassman, Shun, in a blood-boiling fight and ends up falling head-over-heels in love... But, when he goes to confess, he's mistaken as another attacker and must defend himself against the younger boy's lethal strikes! While the fight leaves Kaoru beaten and bruised, he suddenly finds himself being kissed...!? As if that wasn't confusing enough, Shun seems endeared by Kaoru's inexperience with love and agrees to date him, kicking off the start of a terrifying romance!