Responses
I think it was his brother and him age gap. Remember how sensei said he was 15 when he first went to Kurokawa's brother concert? Kurokawa's brother was already an idol then, so I'm thinking the brother is older than Sensei.
I think it should not be age gap. Its the 7 years gap that sensei has been idolizing the brother or only looking at the brother as oppose to the relationship of kuro and sensei which is relatively new.
So in the beginning it was stabilized that the bottom was 22 and the top 18, but then on chapter five there was a panel that said “the seven year gap is huge” or something like that, y’all get the point, was that referring to the gap between Shiba and the pink haired dude or the gap between the pink haired dude and his brother?