Natsu ni Mebuku wa Koi no Oto
Yuu is concerned about the new transfer student, an antisocial boy named Yamauchi. But once he sees Yamauchi smile, he can't help but want to see it again and again. And maybe kiss him as well. [Has other related works, not yet on mangago]
Nise x Koi Boyfriend
1-2, 6-10. Inugami is a shy otaku boy, who dreams of having a fateful romantic encounter with a girl. Luckily for him, a girl shows up right at his doorstep- a girl who looks eerily similar to his popular male classmate Meguru. 3, 11. Keishi asks Yukihito, a stranger, out in a whim. He comes to realize that Yukihito is a sex crazed demon. He loves him anyway. 4. Hanao is a playoy who dislikes boobs, but can't explain why. (He's gay). He becomes interested in Koino, a boy in his year who has a crush on him 5. Hirono became popular to cure his loneliness, but becomes sidelined when his best friend Ogata gains popularity. Turns out Ogata is borderline yandere, but Hirono doesn't mind.
Akai Ito No Shikkou Yuuyo
Keiji possesses the talent of being able to see the red string of fate, so he's elated to suddenly see his own string wrapped around his pinky. He's less excited when he finds out that it leads to his underclassman Hiro, who is a guy. Determined to defy fate so he can be with the girl he likes, Keiji tries avoiding Hiro at all times. But things aren't that simple.
Kanawanu Koi no Musubikata
[Sequel to Akai Ito No Shikkou Yuuyo] Kamisawa is in the business of cutting the red string of fate, freeing his clients of their soulmate obligation. He meets Hara, a businessman, and they become sex friends... Until they realize they've fallen I love. Kamisawa is terrified of Hara finding his true soulmate, but Hara is stubborn and refuses to let Kamisawa go.
Renchin!
Ostracized and lonely, Kami is sure his only good quality is his cooking. When foodie news reporter Waki moves in with him after a house fire, he teaches Waki how to taste flavors, and Waki strives to teach him love
Kurui Naku No Wa Boku No Ban
Takaba is an alpha who refuses to have sex with an omega, too traumatised from childhood memories of his father sleeping with different men every day as sex work. He meets Karasuma, an omega willing to sleep with anyone to climb the corporate later. But he's not quite what he seems
Kiss Shite Yowamushi-kun!
[There isnt any shotacon, i just noticed that tag... the last couple has an age gap but its not underage afaik?] 1-2 Sawa is a college student, who was confessed to by Ono, a high school senior. They work together at the same bookstore, and Sawa might be falling in love with Ono's adorable personality 2 - Yoshihiko is a 31 year old man, who lives alone and wants more zest in life. And then he meets the adorable ghost boy who lives in his house 3 - Hidaka meets and starts dating Leo, a transfer student who moved into his class. It turns out Leo is also the same boy Hidaka relentlessly bullied as a kid (and Leo knows) 5. Kuro is a neko boy, who's master is always thinking about a boy just like him, Akira. Kuro thinks he's a replacement, and is bitter. But that's not it at all
Pinup Boy
Masaki is a straight guy working at a gay bar. His coworker, Hajime, snaps at Masaki's homophobia. Masaki fixes his attitude and ends up fiding out that Hajime wears lingerie, which turns him on. A lot. [Spinoff of some other manga but it looks really transphobic so im not reading it <3)
Koi wa Ina Mono Myouna Mono
On the first day of school, Tamura Masafumi sees Seiwa Narumi and immediately passes out, recognizing him from his reoccurring prophetic dream-- of them having sex. Tamura tries to hate Seiwa, but its really hard to hate a golden retriever boy with a heart of gold
Love Monster (mio Junta)