Summary from back cover:
Synopsis (with spoilers)My name is 赤尾龍太. On the first day of high school, a female in class came to talk to me. "Do you still remember me? My name is 千紗(Chisa? will use this cause its easier to type), I was your classmate in kindergarten. You even assisted me in finding a ring back then." Chisa is a girl that seems a little shy, but she is very cute when she smiles, and her body is well-developed, and so I, Chisa, my childhood friend 有栖, class leader 高槻 shared a wonderful high school life. One day, Chisa's parents died from an accident, in order to console Chisa, I volunteer to help her in any way, yet unexpectedly, Chisa actually made a request as well, requesting me to take over the world with her......!
Spoiler! :