Although Wataru may appear as such, it has been noted by both Shou and Hibiki that he possesses a remarkable aptitude for academic pursuits. Despite his outward demeanor, Wataru is known for being kind-hearted and full of energy. It seems that he harbors a fondness for Mion, despite attempting to portray himself as her protective older brother figure.
He and Mion blush when they are seen together in the recent episodes, so their feelings might be mutual.