If you loved Trinity Seven: Eternity Library & Alchemic Girl, try A Certain Magical Index: The Miracle of Endymion
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.

Trinity Seven: Eternity Library & Alchemic Girl

A Certain Magical Index: The Miracle of Endymion
What they share
Both films are directed by Hiroshi Nishikiori, and they both carry the playful mood tag, and they sit in Action / Animation / Comedy / Fantasy territory. If that's the register that drew you to Trinity Seven: Eternity Library & Alchemic Girl, the second film will land in a comparable space — through a different lens.
What A Certain Magical Index: The Miracle of Endymion is
Technically, it's about a girl with a voice that could trigger an interdimensional quarrel, but mostly it's about hanging out at a space elevator. Touma, Index and a newcomer are enjoying the view when a magic-user shows up to spoil the vibe. All they wanted was a nice afternoon, not a plot device.