it's less of a plot and more of a wonderfully chaotic experiment in polyamory ethics. The main driver is Naoya, who after being confessed to by his childhood friend Nagisa, decides he can't choose between her and his current girlfriend Saki. His 'solution' is to propose they all date each other equally, with everyone's approval. The plot is basically watching this insanely naive premise crash into reality over and over again.
It's structured around these escalating scenarios that test the boundaries of the arrangement—like meeting the parents, dealing with a potential fourth girl (Mirika, who aggressively forces her way in), or navigating school events. The tension isn't really 'will they or won't they' because they're already together; it's 'how long can this possibly last before someone's feelings get irreparably hurt?' The humor comes from the sheer absurdity of them trying to apply fair, logical rules to something as messy as love. I keep reading mostly to see just how far the author is willing to push this before it all collapses.