|Novel Debut||Volume 3:Chapter 10|
|Anime Debut||Episode 6|
Stella dedicates her service to her master, Pegasus. Despite this, Stella tends to put Pegasus in awkward situations by either bluntly reminding him that not being able to introduce one's self is an act of rudeness towards other people, or reminding people (like Kodaka) her master's actual name (which is Pegasus), much to Pegasus' embarrassment. Nonetheless, Stella continues to serve Pegasus with devotion such as carrying out his orders without hesitation.
It is revealed in Boku wa Tomodachi ga Sukunai CONNECT that Stella is actually Pegasus' daughter, making Sena her half sister.
In the light novel, manga, and anime, Sena and Stella aren't seen to be interacting much, but it is greatly implied that they still share a master-servant relationship. Considering that she is Pegasus's daughter, Stella serves Sena just as the former does to Pegasus. Likewise, Stella takes care of Sena's whole appearance, such as her hair, make-up, and clothing among others, and also does her shopping.
Stella seems to have a liking towards Kodaka, as she usually teases him in various occasions (e.g. giving Kodaka a condom in the middle of his study session with Sena). Regardless, the relationship between the two is seen as normal.