(I feel like I need to give them a bit of fluff)
Oikawa had gotten sick. And for what Iwaizumi had thought as of the dumbest reason.
It had been raining after practice and Iwaizumi had headed out first- and Oikawa didn't let him go till he took his umbrella. Thinking that Oikawa had an extra umbrella in his locker or something he agreed and took it.
Only for the next day to be found out that Oikawa ended up sick. Why? Because he walked home in the rain. He didn't actually have an extra umbrella but knowing Iwaizumi had forgotten his he didn't want him getting sick.
So of course Iwaizumi took it upon himself to take care of his best friend as he was home alone and he didn't trust a sick Oikawa left alone for the weekend.
And a 'fun fact' he'd learned during this weekend was that Oikawa was extra clingy when sick and feverish. Going from delusions-Oikawa insisted that Iwaizumi had to go pet his cat before it died of sadness... neither have a cat- to Oikawa demanding cuddles and throwing a fit.
