HoYoverse revealed during a livestream for its Honkai: Star Rail game on Friday that it and MAPPA have co-produced an "animation concept trailer" for the game. The trailer, viewable below, is titled "Death in the Afternoon."

Yuzuru Tachikawa (Mob Psycho 100, Death Parade director) directed the trailer and Kayoko Ishikawa (Sarazanmai, ZENSHU.) was the character designer. The end of the above video features the words "MAPPA Honkai: Star Rail Animation A New Story Awaits."

The HoYoverse staff had introduced the video in the livestream as a "mysterious collaboration project." HoYoverse's press release about the livestream announcements stated that at the end of the livestream, "...the original animation project co-produced by HoYoverse and MAPPA premiered its concept trailer, 'Death in the Afternoon.' Please look forward to the continuing cosmic adventures!"

The livestream and HoYoverse's press release did not give any further details. It is currently unclear if the "original animation project" is the above trailer, or if the collaboration will include other works.

Update: ANN reached out to HoYoverse for clarification, and the company provided the following response:

HoYoverse launched its Honkai: Star Rail game for PC and mobile in April 2023, and then for PlayStation 5 in October 2023. The game has exceeded 150 million total downloads across all platforms.

HoYoverse describes the story:

The game will launch its Version 4.2 patch on April 22. The patch will celebrate the game's third anniversary.

HoYoverse's earlier game Genshin Impact launched a "long-term collaboration project" with ufotable in 2022. The project is still in production.

Sources: Press release, Honkai: Star Rail game's YouTube channel (link 2)