Usagi Otoko Tora Otoko
Riichi and Uzuki meet when Uzuki, a surgeon at a Uni, finds Riichi with a gunshot wound in the middle of the night on his way home from work. Uzuki runs away since Riichi scared him but comes back and patches Riichi up. Riichi seems to fall in love with Uzuki but he was out of it and believes that "Suzuki" is a girl and searches the hospital for Uzuki who ends up being the doctor who is placed under Riichi's friends care. Later, Riichi realizes that it was actually Uzuki whom he fell in love with and attempts to see if he is a girl by putting his hands down Uzuki's pants only to find a penis. Riichi proceeds to punch him but for some reason, he can't since Uzuki reminds him of a rabbit and small animals are his weakness. Riichi falls head over heels in love with Uzuki even though he's a guy. Uzuki eventually comes to love Riichi but doesn't really do anything because being in a relationship with a yakuza comes with many difficulties but they eventually kiss and do some adorable things and OHHHH LORDDDD their size difference bless this mangaka really. It's almost complete but still has some translating to do and the 3rd volume onwards doesn't have great scans but it's okay since these two are sweetie pies.
Wonderful Days?