Q.E.D. - Shoumei Shuuryou

Q.E.D. - Shoumei Shuuryou is a manga series by KATOU Motohiro.

Plot
Touma Sou graduated from MIT, but he comes back to Japan because he wants to know how it feels to be a high school student. On the other hand, Mizuhara Kana is a strong girl who loves sports. Together, they are partners in solving cases that happen around them.