At the start of the movie they didn’t have their loveracelets.

Then Yumoto, Atsushi, Io and Ryuu got caught up in a fight after meeting up and got theirs.

He has some kind of power to gain and lose weight as he wishes (don’t ask me what the lore behind that is about, I don’t know either…)

Edit:

They only appeared in the last part of the movie and ended up soaking in the onsen with everyone before returning back to their planet.

Atsushi is working as the head manager of the Binan city office tax department now.

Yumoto asked him for help to find the others by using his position to search up their home addresses on the city tax system, and at first Atsushi wasn’t willing to, but then he realised if the Battle Lovers couldn’t reunite -> The world would end -> he wouldn’t be able to eat curry anymore, and Atsushi caved in.

Kinshiro was manipulated/influenced (?) by Aye Aye and was arguing with the Boueibu about not wanting to take baths.

At the start of the movie Yumoto had no way of finding where and what the senpais were up to 10 years later, but he ran into Akoya who had been keeping in contact with Io, Ryuu and Arima and they got reunited as a result.

(I'll try to make the spoiler as vague as possible so I don't spoil the entire story...)

Nobody recognized the shaggy version of Enchan except Atsushi

Kinchan's current occupation is a mystery but Arima seems to know what it is and plays along with it

Kinchan and Atsushi try to make awkward small talk again, with Enchan egging Atsushi on

By the way

Not as strong as whatever the third years had going on but yes!

The usual ioryuu friendly bickering (Io worried about Ryuu's savings and Ryuu commenting on how lame Io's clothes look)

The two of them possibly kept in touch for the past 10 years (implied but not confirmed though, or it could just be my ioryuu goggles put on too tight)