Suddenly had an idea for a character that is essentially a background character. People would be able to socialize with this character, and this character would always be with the group. But they wouldn't have a personal sub-plot. Their backstory would be rather shallow and boring, only highlighting a few memorable moments that would be rather average compared to the rest (such as a their first kiss, first job. Boring, average stuff). Along with making them non-romanceable, or just very hard to romance. They also wouldn't have severe personality flaws, maybe just some depression or something. Maybe give them a hobby or favorite pass time. They may have some good advice for keeping the others going through hard times.
TL;DR I wanna make an average joe that never really enters the spot light, and only helps others with personal sub-plots while not having one of their own.