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a brief spoonfeed for those who have never seen a game in development:
what you're seeing now is called proof of concept, it's pourpose is show what kind of game it is, how it looks, and it's gameplay mechanics.
things like animation cycles, UI and sound effects are usually generic placeholders that will be replaced in the future.
by revealing a proof of concept to the public they are providing reasons for new artists, programmers and investors to have interest in joining the project, considering the massive popularity of Hololive it's safe to assume it's gonna work, unlike other indie developers who can only rely on crowdfunding and luck.