Since Iwaizumi and Oikawa are childhood best friends, they knew each other a little too well sometimes

Iwaizumi knows where is Oikawa at each time, no mistakes, never

That shocked Makki when he asked where's Oikawa during class breaks and Iwaizumi simply answered Makki that Oikawa is in the toilet without even thinking

Makki went to the toilet and gasps as he saw Oikawa walk out
"Is Iwaizumi a stalker?!?"
"Huh wat r u saying Makki?"

Makki and Mattsun then try for a few more times and every single one is correct OMG

As for Oikawa, he knew where Iwaizumi keep all his things when Mattsun dared him to hide Iwaizumi's favorite underwear Oikawa went into Iwaizumi's house and took it out even tho that underwear is hidden in a place is impossible to find

Btw they got each other's house key for "safety purposes"

Mattsun and Makki mind blown

This idea is weird but its kinda true since they've been together for so damn long