a character hikikomori can identify with?

I'll point out two major things that are supposed to be his "annoying" characteristics that most likely led him to be a hikikomori: "stop going to school/work and stay at home for longer than 6 months without social interactions (except for his/her own family)" by MHLW definition.

1) Active-type of Communication disorder

He may sound alright in English subs, but Japanese people see that he cannot always communicate well in Japanese society. His annoying talk (and he just talks too much and not funny) drive people away. He is almost always too excited, which also annoys others. He is smart and knows a lot of tough idioms too that don't make sense to others, but he still uses them in his talk no matter others understand him or not and that annoying too. It shows he has a high chance of failing in communicating with others, especially at school, and especially in Japan. (I'd say he is probably alright making friends in a foreign country.)

2) KY (Kuuki Yomenai = cannot read air) One cannot guess others' intentions or consideration, and say things he shouldn't say or does things he shouldn't do. "Reading air" is often considered by many young people to be the most important communication skill in Japan.

He sort of belittles himself and describes himself as KY and claims it as his power. Nobody is supposed to be able to open the door to Beako's library, but he thinks he can because of his nature he says (no matter what the true reason is). He claims he has been told so by others that he always appears at the wrong place at the worst time where/when others don't want him to. Or he points out things that others avoid to say or purposely don't mention out of consideration or sympathy. This behavior can destroy the friendly atmosphere and people may learn to stay away from him.