Doujinshi circle. Crimson is also the name of the main artist herself. The illustrator of Aoi Sekai No Chuushin De.
Her works are well-known for distinctive meme-ish phrases.
For example: "くやしい...! でも...感じちゃう...!" or "ピクンピクン".
Pen-name: クリムゾン (Crimson)
Circle name: クリムゾン (Crimson) or クリムゾンコミックス (Crimson Comics)
Old circle partner: カーマイン (Carmine)