Slightly delayed (under possible cover of Letters to the Lantern!), it's First Times (HP/DC): First Titanfest.
https://archiveofourown.org/works/462211.../136603516
tealruby Wrote:Now she really gets how Wally had felt when she brought him to meet her oldest friends…
Wally’s mentioned this event recently. He’s been to gatherings of her friends, and now he’s taking Hermione to one of his. Quite a different group of people than those in the League. For one, many grew up together. For another, they’re more than friends. They’re family. Oh, and they’re all closer to her own age, which is refreshingly nice.
https://archiveofourown.org/works/462211.../136603516