Nat-chan no Akai Tebukuro

Based on a book by Nishino Ayako. A story about the atomic bomb dropping on Hiroshima. Elementary schooler Nat-chan moved to Hiroshima and was knitting red gloves her male friend Shun-chan. The bomb hits and she dies. Shun-chan now an adult reunites with Nat-chan's remains via her shadow (nuclear shadow that is, where her body vaporized leaving an outline).