If you loved Grave of the Fireflies, try Only Yesterday
A bridge between a film you've already seen and one most people haven't. Only Yesterday has roughly 5.2× fewer votes than Grave of the Fireflies — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.
What they share
Both films are directed by Isao Takahata, and they both carry the bittersweet, foreign gem mood tags, and they sit in Animation / Drama territory. If that's the register that drew you to Grave of the Fireflies, the second film will land in a comparable space — through a different lens.
What Only Yesterday is
Here's a film that asks, "What if your fifth-grade self judged you?" A woman in her late twenties goes to the countryside, reflecting on her childhood. It's a Studio Ghibli production for people who find Studio Ghibli a little too exciting.

