It's "Genos"- [ The gauntlet disappears from Saitama hand in flash of light, and forms into familiar form of a teenage cyborg next to him ] -that triggers the change back.

[ He's excited, looking around, the job well done.. and so epicly at that! Yeah, he just turns blind eye to the collateral damage ]

Yes, let's check on them. But first- [ he walks around Saitama ] - can you show me your other hand?