@KuroeNekumi I think that a lot of the thick-headedness he has around the name has probably been that he never really knew anything that it related or linked to. It's only standing in front of her grave, understanding what reaper means, and her own words here that basically made things click.
Either this was the wham chapter the author built up to all along, or it started as just a fluffy manga about an idiot with a good heart and the author came up with this angle on the fly. I honestly don't know what would impress me more.
@Kaeos999
it's not that he was clueless, Young boys like him are innocent kids that prefer to show their interest to someone in a roundabout way... Just like how a boy tends to bully other people just to get close to them. In his case, he justify getting close to her because she's a "cool reaper" when in fact she just like her a lot.