Senjuushi: Kijuushi-tachi no Happy Birthday!

Senjuushi: Kijuushi-tachi no Happy Birthday! is an original video animation released in 2019, serving as a spin-off to the Senjuushi: The Thousand Noble Musketeers television series produced by TMS Entertainment. The project originated from a mobile game developed by Marvelous, which anthropomorphized historical firearms into characters known as Musketeers. This OVA was created to expand the narrative world of the franchise by focusing on a lighthearted, slice-of-life celebration of the characters' birthdays.

The production utilized the existing aesthetic established by the television series, emphasizing the detailed character designs that were central to the series' marketing. As a niche title within the broader otome-adjacent media landscape, it was received primarily by the established player base of the mobile game. The animation team focused on character-driven interactions, aiming to provide fans with a dedicated format to engage with their favorite designs outside of the high-stakes conflict depicted in the main game and television storylines.