Kuudere (クーデレ; pronounced [kɯːdeɾe])is a Japanese term for a character who appears to not have emotions. They are often stoic and expressionless, and they remain calm in stressful situations.[1]

2B, a popular kuudere character
In contrast to tsundere and yanderecharacters, whose archetypes revolve around change in their behavior, kuudere characters often keep the same core traits throughout a narrative. Other kuuderecharacters traits include being aloof, being level-headed, and serving as the voice of reason during conflict.[1]
The word is derived from the words "cool"(クール, kūru) and "affectionate" (デレデレ, dere dere).[2] The term refers to one of four popular Japanese character types, the others being tsundere, yandere, and dandere.[3] Rei Ayanami of Neon Genesis Evangelion is thought to have played a major role in the popularization of kuudere
from https://en.wikipedia.org/wiki/Kuudere