The original light novels' title translates as "Listen to me girls, I am your father!" (I dare you say that with a Darth Vader voice to some RL schoolgirls!), so you can imagine the kind of "seriousness" contained within their pages... 7 volumes have been published so far by Shueisha; they are authored by Tomohiro Matsu (Mayoi Neko Overrun!) and illustrated by Youhei Takemura, with a story that follows a university student who has to live with his sisters' three daughters: a 14-year-old tsundere, a 10-year-old little demon, and a 3-year-old small girl. Fun times!...
A shy local gallery is up already, and below is MAL's synopsis for the light novels.
"Segawa Yuta is a freshman of a university. He lost his parents when he was small and was raised by his sister Yuri. Yuta has been living alone since Yuri got married to a middle aged man when Yuta was a junior high student. One day, Yuri visited Yuta's apartment and asked him to take care of her three daughters while Yuri and her husband were on a trip. He unwillingly accepted the job but the plane Yuri took went missing. In order to prevent the daughters from being adopted separately by the relatives, Yuta decided to take in all the three girls. A life of a strange family in a tiny apartment begins."