Oh, that's a fun idea. I'd probably write the two not realizing it was a nude beach until they already got there, and deciding this is their last chance this summer to go on the beach together and nervously taking their clothes off in the same changing room. Cue panic between the two, mostly Legoshi, and when he leaves the changing room, Louis is there waiting to use it and sees him. Cue second panic. Story ends with Legoshi and Haru musing on if it was worth it or not.

It's a rough draft, I could probably smooth the edges a bit more.