Had this funny idea that the Four Heroes have their own version of shouting "Marco" and answering "Polo", inspired by this meme
And while Naofumi's world has, and he knows all three versions, the other three only have one each. And because Naofumi's the least likely to get unintentionally lost, he's also usually the one shouting first.
So, things are happening during a Wave, and they need to regroup, but there's too much chaos and fighting and environment to figure out where everyone is. So Naofumi just shouts "WAKE ME UP" at the general surrounding area.
Three answers pop up from completely different directions, each increasingly panicked.
"WAKE ME UP INSIDE!" Ren shouts as he finishes cutting down a monster
"WHEN SEPTEMBER ENDS!" Itsuki yells, shocking his party members enough for him to quickly land three hits.
"BEFORE YOU GO GO!" Motoyasu screams as he dodges another monster attack
"Ah, there they are." Naofumi comments