Mon Seul

Mon Seul (モン・スール, lit. "My Happy Way of Life") is a manga series by Akira Kizuki. It was serialized in Comic Gum.

Plot
After their parents divorced, mother remarried, and father ran away, the remaining two members of Ikeuchi family -- college student Masaki and his younger sister, elementary schooler Minami -- along with Masaki's roommate and best friend Kanda, barely support themselves under the same roof. While the difficult yet happy life seemed to continue forever, all hell broke loose when Masaki one day returned home from his part-time job earlier than Minami expected.