(idk if ur asking for his last name, it’s suzuki) but maybe it’s just cuz kalego has been keeping a special eye on him considering he’s the chairman’s “grandson” and has had personal experiences with him. but now that i think about it i can’t remember the last time anyone has called him suzuki-san or sumn, it’s always “iruma”, you bring up a valid point !
It would've been odd if everyone would call him by grandpa's last name. Also, since the beginning he was also so outgoing and the friendly manner grandpa showed him; made everyone know a "last name" wasn't needed.
Am I the only one bothered that Iruma has no surname? Especially on that student list at the last page.