In The First Grade - Vol. 2 Ch. 14 - When everyone went to the ofuro (last part)

[MangaDex]

 

[Gredias]

>That backstory
Is that a motherfucking JoJo reference?

 

[rsross2]

There's several JoJo's Bizarre Adventure references throughout the whole series, so probably.

 

[Alex-dono-sama]

nekid grandma

 

[Jelly_Storm]

Nobody gonna comment that this guy looks at his arse while having a wank huh?

 

[SpecialProjectY]

Can't imagine the mental scar Iori got after seeing that view, if it instantly gave him the chills.

Crisis avoided, but Sasara fell even more in love...

 

[BakedBanana]

"It appears whenever I take a bath or my body temperature rises." (Page 3)

Okay, I suppose that makes sense of why we haven't seen it until now. Though kinda weird, never heard of scar that work like that (unless it was something like a burn scar).