Okay. Typical Japanese novel of hero summoning, except that the dudes been summoned back twice or he's been summoned hundreds of times to different places before. He gets summoned and finds that his classmates have been cursed so he puts his hands and fingers into a gun like shape and pretends to shoot, presumably shooting out purifying magic or something of the sorts. At the start he gets placed into the castles janitor room instead of the noble rooms. The queen finds out he's a super powerful dude that can most likely destroy the nation with ease and is not one to get on their badside with. That's all I can remember, in fact I could just save all the novels I read on the novel updates tracker, but it's trash and i didn't save it in my novel tracking app at the time. I could probably find out just as easily by just using the 'summoned hero' or something similar tag to find it quicker than writing this but hey. EDIT: FOUND IT. 100 times was an exaggeration, sorry about that. Had a Lil memory loss there. It was the 'Hero? No I am an ordinary citizen!' novel. Thank you.
Hmmm sorry but while I have seen the "summoned hundreds of times" premise before, it had none of that other stuff.