Color (mimori Ao)
https://www.mangaupdates.com/series/yyu5wb7/color-mimori-ao
Colorful Line
https://www.mangaupdates.com/series/25cn1dc/colorful-line
Concierge No Koibito
This isn't a oneshot. There's a full volume. Chapters: 1. Concierge no Koibito 2. Wakadanna no Koibito 3. Shachou no Koibito 4. Bishokuka no Koibito 5. Shodouka no Koibito. I've only read the first chapter available.
Oboreru Knife
This manga had me throwing stuff everywhere. I understand that kou and natsume had a bond deeper than love itself. But bruh, WHY DID U DO OTOMO LIKE THAT, I was already so fucking happy, even if that psychotic b**ch ended up with kou I would've accepted it. The ending was okay and the characters were all very interesting. The development in each characters and their relationships with each other was shown very well. The plot was unique and the story mind blowing. And reading this manga also made me realize how authors back then we're all unique and made very interesting mangas. Nowadays it's all just isekai. It was a breathe of fresh air. Overall this was a great journey
Cor Leonis - Shishi No Sinzou
https://www.mangaupdates.com/series/822qd22/cor-leonis-shishi-no-sinzou
Cosmic Color
https://www.mangaupdates.com/series/x6cn77a/cosmic-colour
Count Down!
https://www.mangaupdates.com/series/lmpuaue/count-down
Count H
Second volume of the Count series. https://www.mangaupdates.com/series/qvolri8/count
Count 0
First volume of the Count series. https://www.mangaupdates.com/series/qvolri8/count
Heat and Run