‘Unexpectedly’/‘it surprised me’/‘more than I thought’— Spinner never imagined he would care for Shigaraki (and the League), see. He joined not even for Stain, exactly, less the ideology and more the feeling that Stain inspired in him; he joined as a last ditch effort to do something with his ‘not worthwhile’ hollow shell of a life, to finally feel something in his empty heart. (And even then, six months after joining the League, he was still aloof and frustrated and not of the best opinion of his comrades because they were second best after Stain lol.)
But now Spinner found himself as deep into the fold as Twice had been, this group of strays that found in each other a place to belong. And though it may have been Shigaraki’s empty horizon speech that got him willing to give his leader a second look, Spinner reveals himself when he says he bonded with Shigaraki over games and stuff? The non-League, non-Stain, non-rage, non-‘work’ things. The trivial, silly, personal-hobbies-likes-and-dislikes things. Idiosyncrasies the both of them have. Friends things that Spinner surely must have missed out on as a bullied, shunned kid and hikikomori.
Spinner didn’t expect to find friends, but he did. He didn’t expect to like Shigaraki as a person, but he did. He didn’t expect to be happy, I don’t think? But he ended up finding something like that.
And now probably, he didn’t expect to miss and worry for Shigaraki as much as he does.