Have you considered looking at other Japanese literature or media for similar characters? For example, Tomoko Kuroki from the manga and anime series "Watamote" is a shy and introverted character who struggles to make friends and fit in with her peers. Another character to consider is Haruhi Fujioka from the manga and anime series "Ouran High School Host Club," who is initially portrayed as a quiet and reserved character before becoming more confident and outgoing.