Kūko (クー子, also known as Kuuko and Cthuko) is one of the main characters, and an alien who is in love with Nyaruko despite that her race is the archnemesis of Nyarlathotepians, and she appears to be clingy. A female Cthughan (alien from Cthugha). She takes the form of a slender, red-haired girl. She is in love with Nyaruko despite that her race is the archnemesis of Nyarlathotepians, and appears to be clingy. She is hostile toward Mahiro and threatens him to stay away from Nyaruko in the beginning of the story. As the story progress, she becomes more friendly towards him. She transfers to Mahiro's school and takes the name Kūko Yasaka, Nyaruko's "wife". She is also obsessed with otaku culture and video games. Kūko was Nyaruko and Hasuta's space elementary school classmate and appears to at the same age as them, although she became a NEET after graduating from high school, and become a Space Defense Agency agent and colleague to Nyaruko later by using the relationship of her uncle who is an employee in the human resource department of the Space Defence Agency. She concealed her feelings for Nyaruko from her family and lied to them that Mahiro is her fiance, as love between Nyarlathotep and Cthugha are considered a shame of the family among Cthughans, however she has displayed having feelings for Mahiro. She possess the power of fire, able to control fireballs, heat, or drones that fire lasers; she refers to them as space CQC - Cthugha version. Her strength in combat is lower than that of Nyaruko's. Her combat form is covering her lower body with red fire patterns.
While her original form as an alien remains to be seen, her from throughout the series is always a teenage girl with two long ponytails that fall down to her waist in length. Her eyes are red as well, a sign of her lineage as a being that can control fire. Her skin is somewhat pale, although whether it is a side effect of her gaming or intended is unknown.
When she first appeared, Kuuko was apparently not wearing clothing. Instead, she was clad in nothing but some sort of red flame-like marks that made up her body. Whether they are actually clothes or part of her body is arguable, but they appear on her body when she activates her Space CQC. She also keeps her hair up with two black clips shaped accordingly to her fire element.
When she is at school, she is constantly wearing the same uniform as the rest of the female students. That is a light blue long-sleeved coat with white accents. She also wears a pink bow tie and black knee-length socks.
Kuuko has a very interesting persona, as her love for video games are quite unlike one would expect of an extraterrestrial. She has little care for the fact that Nyarko is of another race that has had bad blood with hers, instead choosing to defy her lineage for the sake of her "love". She is a kind person at heart, but can be extremely perverted when things get out of hand.
Kuuko is a Cthugan, a race of aliens who are capable of easily controlling the element of fire. As such, she is capable of manipulating flames and bending them to her will. This is one of her most important defining aspects during actual combat with other aliens.
Kuuko is from the Intergalactic Space Defense Agency like Nyaruko, and she withholds her own powerful form of Space CQC. However, her version of Space CQC is unlike Nyarko's. Instead of real hand-to-hand combat, which she is also proficient in, she is capable of summoning small red drones from an unknown point on her body that are linked to her mind. She is capable of moving them as she wants and have them fire powerful lasers with unlimited ammunition, making her a powerful ranged ally to the close-ranged Nyarko.
To say that Kuuko is "in love" with Nyaruko is not an exaggeration, although her sexual deviancy tends to leak out and have her say highly inappropriate things sometimes. What exactly made her fall for Nyarko is not known, but she seems to love her enough to spend a lifetime and more with her. Unfortunately for her, Nyaruko does not share any shred of compassion or reciprocation towards her out-of-place feelings. This leads to constant comic relief among the group.
They were once on somewhat hostile terms, what with Nyaruko loving Mahiro over Kuuko. This led to the initial attempt and desire to obliterate him off the face of the universe. However, after Kuuko began residing in the household, the two have become good friends. Despite their history, Mahiro finds her a reliable person save for her love of video games. He has come to respect her as a friend and as an equal.
At the start of her homestay, Kuuko became mere acquaintances with the human boy. However, at the end of Season 1, her somewhat twisted desire to marry him out of her want for Nyaruko became apparent. In the 2nd Season, she grew to like him as more than a friend. Now, she likes Mahiro to the point where she would like a family to blossom between him, Nyaruko and her.