If you loved A Certain Magical Index: The Miracle of Endymion, try Magic Tree House
A bridge between a film you've already seen and one most people haven't. Magic Tree House has roughly 6.5× fewer votes than A Certain Magical Index: The Miracle of Endymion — 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 Hiroshi Nishikiori, and they both carry the cozy, playful mood tags, and they sit in Animation / Fantasy / Science Fiction territory. If that's the register that drew you to A Certain Magical Index: The Miracle of Endymion, the second film will land in a comparable space — through a different lens.
What Magic Tree House is
Apparently magic tree houses are a thing now. Jack and Annie find one and use its books to travel through time. It all gets a bit complicated from there obviously.
Ask 
ChatGPT
Claude
Grok
Le Chat
Perplexity
for a deeper bridge
ChatGPTClaudeGrokLe ChatPerplexity