Ichido Dake no Uta
Short sequel to the original story
Kimi ni Sasayaku Mirai
Starts with Senpai x Kouhai couple, but the senpai died in a plane crash. He came back in spirit to be with the Kouhai for one last time, which was sad, but he immediately re-incarnated into a younger Seme to be with the Uke. You could say he's the obsessive yandere type. Other stories as well.
Boku Dake No Kimi, Kimi Dake No Boku
Childhood friends with a bit of an age gap. Uke is very manly, a famous model who's chased by both men and women, but he will toss everyone and everything aside to be with his childhood hero, friend, and crush, who he thinks will never return his love.
One Little Wolf Falls in Love
Mutual love. Two people sneaking glances at each other in the morning train they share. Plus a touch of supernatural - Uke is a half werewolf who involuntarily transforms every day after sunset, so even though he wants romance, he knows he can’t have one due to his body conditions. Seme is good looking but has never been in love either, until he meets the cute and innocent Uke
Namida no Priceless
HOT AF! Seme (younger) is extremely genuine and passionate, but he is a complete sex god in bed. He says some WILD shit to the Uke who's completely at his mercy even though he's the older one. Their chance encounter on the delayed train lead them to find each other in their lowest time, it's a beautifully written plot and equally loveable characters.
Tasuketa Yakuza ni Nerawaretemasu
Yakuza boss who actually doesn't want to live that lifestyle anymore x Taxi-driver who's been living a normal, typical, boring life. Their relationship starts out physical, but the Seme def fell for the innocent Uke first, and wishes to leave his responsibilities to be with him.
The End of the World, With You
Seme was a serial cheated, quite blatant about it too. Frankly he didn’t know what love is so he didn’t understand the weight of betraying someone’s trust. It took a literal end of world in 10 days scenario for him to attempt to reconnect with the only person he might have truly loved but didnt realize it then
Yurusareta Uta