Aikagi 3

A spare key hanging around a girl's neck is the whole problem: Yuuto comes home to find his childhood friend Saotome Ai already inside, phone in hand, treating his house like her own. She calls him senpai, ignores every complaint, and has no intention of giving the key back.

The story follows how that arrangement turns into something more, tracing the shift from a teasing, familiar closeness between the two into an actual romance, with Ai as mischievous as ever and Yuuto perpetually a step behind her.

There's no branching to manage here, just a fixed story to read through at its own pace, told in Japanese-style visual novel form with voiced dialogue carrying the back-and-forth between the two leads. The school setting and their established history do the work of building intimacy scene by scene, moving from awkward routine toward the more explicit stretches the game is clearly building toward, all rendered in 2D character art rather than animation.