The joke is that Naoya says yes to both of them, and the show commits to that bit so hard it becomes genuinely hilarious instead of creepy. Traditional harem anime wastes time on guilt and indecision; this one just removes the indecision entirely and builds comedy from the actual chaos of dating two people who somehow don't hate each other. It's dumb on purpose, it knows exactly what it is, and if you're willing to laugh at a premise instead of think through it, the comedy timing carries you all the way through.
Naoya finally has everything he wants: Saki said yes to dating him, and he's riding high on the rush of new love. Then Nagisa appears with a confession of her own, and instead of turning her down like any reasonable person would, Naoya makes a choice that will complicate his life in spectacular ways. He decides to date them both. What follows is pure chaos dressed up as romance. Naoya has to keep his double relationship secret while managing two very different girlfriends with competing needs and personalities. Every stolen moment with one requires elaborate cover-ups from the other. Every date becomes a high-wire act of scheduling and deception. The comedy comes fast as situations spiral: missed calls, convenient coincidences, and the constant pressure of being caught. Beneath the absurdity sits genuine heart. These aren't cardboard characters, and Naoya's predicament explores what happens when someone refuses to choose, when indecision feels easier than honesty. It's lighthearted enough to laugh at, but grounded enough to question whether anyone in this scenario can actually get what they deserve.