eldelita (rakurakutei ramen)
An original character by Rakurakutei Ramen.
Usually just called "Elly", she is a "Last Boss" and "Demon King" (Maou/Overlord, like Laharl from Disgaea). She was beaten by Seren (via direct meteor strike headshot) and forced into being Seren's apprentice.
Elly is chronologically a very young child, but physically adult and relatively emotionally mature (especially by Karindou standards). She has a rather enviable figure... which often is overtly envied. In spite of this, she is a "purehearted child" (in fact, one of the very few Ramen characters who can claim anything of the sort) and would rather just unassumingly get along with others.
Elly is also now a classmate with Tamaryu and Ran, and whose teacher is Shizuki in the new Youkai school that opens up.