X Equals: X wa Nazotoki ga Osuki

There is also a thrilling mystery to solve! Kai Kunieda is a bit of an oddball, but he is known as "Mr. Holmes" for his extraordinary powers of deduction. Kii Hosaka secretly has feelings for "Mr. Holmes". Kii became Kai's partner with her overwhelming feelings and enthusiasm, but it seems that she is only his partner for detective work, nothing more... Still, Himegi is not discouraged and strives to convey her feelings to Kai someday. Mysterious incidents are constantly occurring around the two of them... They somehow manage to solve them with Kai's analytical skills and Himegi's initiative. (Source: Shogakukan, translated)