Joahaejwo

Hyo-Jin, a rabbit, takes in Ji-Ha, a black panther, who was abandoned, and raises him like his own younger sibling. Ji-Ha, who grew up quickly, confesses his love to Hyo-Jin every day as soon as he becomes an adult, but Hyo-Jin rejects his confessions every day. Then one day, Hyo-Jin goes into heat for which he was not prepared for, and Ji-Ha offers to help Hyo-Jin, who doesn't know what to do...

"I'm an adult now. I'll help you."

(Source: Lezhin, translated)