Oikawa only knows y/n aka Mikuni as his sister but didn't know that he has another sister (Tomoe) that's a secret who's is living her own life and dating his best friend (Iwaizumi) behind his back or y/n dating Raiden who is his rival & best friend behind his back or even that y/n is engima as he thought y/n are a normal omega like him, makki, kunimi, Yahaba & the other omegas in other teams who thought the same but also show you more respect than him. And he doesn't know that mattsun & Makki are together either about kindaichi & Kunimi being together, kyotani & Yahaba being together cause they are doing everything behind his back. And they are all mates. Iwaizumi & tomoe are mates, y/n & Raiden are mates, Mattsun & Makki are mates, kindaichi & Kunimi are mates, kyotani & Yahaba are mates.