Issho Watashi No Joshu De Ite!

Issho Watashi No Joshu De Ite! summary:

"The relationship between a detective and their assistant is not unlike romance!" Due to his natural tendency to assist others (a "helper type" personality that makes him constantly want to lend a hand), Mitomo Tasuku had always lived in the shadows. To break out of this, he made it his life's mission to "become number one." However, at the high school he transfers to, he encounters three detective girls, who happen to be his rivals from elementary school with whom he formed a detective club together. Thus begins Tasuku's fierce battle for the top detective spot! However... these girls seem to harbor passionate feelings of a different kind...!?