Considering the "WHA" on their outfits, which I've seen some speculate to be "World Hero Association", it's possible we might be seeing them travel overseas. I'm also really curious how much of the "Three Musketeers" allusion they'll lean into, or if it's just a reference to refer to the main 3. Like you mentioned, if the "He" will be their D'artagnan, will they face a Robin Hood-esque villain (could lead to them expanding more of the Oji Harima lore)?

I just have this funny image in my head of them hearing someone say "All for one and one for all!" and Midoriya gets incredibly tense and scared and they're just like "What you never read Dumas?"