If you loved The Door Into Summer, try Toki no Tabibito -Time Stranger-
Eine Brücke zwischen einem Film, den du schon gesehen hast, und einem, den kaum jemand kennt. Das teilen sie, und was der zweite macht, was der erste nicht macht.

The Door Into Summer

Toki no Tabibito -Time Stranger-
Was sie teilen
Both films are directed by Mori Masaki, and they sit in Animation / Romance territory. If that's the register that drew you to The Door Into Summer, the second film will land in a comparable space — through a different lens.
What Toki no Tabibito -Time Stranger- is
A rogue time-jumper with a broken stabilizer turns modern Tokyo into a waiting room for history’s worst day. His unwilling passengers include four pupils, a teacher, and an obsolete van, all dragged through the firebombing of 1945 before arriving smack in the middle of Japan’s civil war. The neatest paradox is that none of them thought to pack snacks for 450 years of sightseeing.