Harmen means a love group based off one person, basically a person who has multiple love interests or lovers, in this AU all the Hashira are in love with you, you are basically a main character

Muichiro: little cloud whatcha doing TwT

Tengen: She's just playingaround. ~

Giyuu: cute af.

Shinobu: oh my, she really is cute ^^

Geyomei: what is she doing? I'm blind remember I can't see.

Mitsuri: So womenly! >/////<

Obanai: Mitsuri is such a simp.-

Senemi:How could you not simp for her.