Blood Suckers

The Blood Donors is a fan-term used to refer to a trio of Ricchii, Yatsume, Mosukii, along with Curie whose shared racial trait between them is that they feed on blood to survive.

The trio consists of the unnamed Mosquito-girl, the unnamed Lamprey Mermaid-girl and the unnamed Leech-girl, all of whom debuted in Chapter 49 of the manga. Following the Extra Species Cultural Exchange Exhibition it is shown that the three girls, plus Curie, live together in their own apartment.

Trivia

 * Yatsumeunagi is Japanese for lamprey eel.
 * The unnamed mosquito-girl is dressed like Shimakaze from.
 * In her introduction, the unnamed mosquito-girl was originally shown to have only two arms, but later in the Omake, as well as the second OAD's endcard, she is shown to have four arms.
 * This was eventually corrected with Volume 12's release, where the mosquito-girl is consistently depicted with four arms.
 * Okayado states that their first appearance in chapter 49 was very incomplete, and as an apology, he asked fans to choose to be one of the male background characters that appeared in the chapter (that's why they all had numbers). He added them in the final release of the volume, along with fixes on the girls: a more gyaru mosquito + two more arms; a more shiny leech + some sort of eye emojis on her face; more makeup for the lamprey girl.