Anime-based video games tend to be aimed at the fans of the series, which makes sense, aiming to offer more content for the show and the characters they love. Similar to titles like Sword Art Online, they either offer the same story arcs as the anime but let you live them yourself, or they allow you to experience an entirely new adventure one that expands on the already crafted universe from the manga to an anime and then a video game.
Black Clover: Quartet Knights prefers to take the latter and opts for an all-new story path that it sends you down, one which takes place in the early parts of the anime when the team are investing a new mysterious dungeon. This means all the main characters and teams are already in play. For the new story, it also means new gamers or watchers of the show will not be tip-toeing around to avoid spoilers or daunted at trying to get a lot of backstories before they dive in.
Yami is turned into a teenager after fighting the first boss, his memories also going back to the moment in time matching his new younger looks. He is looking for someone called Karna, who once they meet up with also looks as she did in the past. The team must uncover why Yami and Karna have regressed and stop Karna from what she is planning based on what happened to her in the past.