The Three-Body Problem

Briefly about The Three-Body Problem manga:

A collection of light novels and special stories by Otsuka Natsuki and illustrated by Kururi.  This collection contains the three part of the story The Maou and I, in which our protagonist encounters the Demon Lord, which she first met as a small black beast. These stories go deeper into Lilia's daily life with the Maou, and how the two of them grow closer together.