This time, Marisa Kirisame goes out alone to investigate (and collect). It is a game in which Marisa is the main character, which is surprisingly rare.
Unlike Touhou 18, this is a game in which you collect new cards and repeatedly challenge stages while conquering stages that develop at high speed and at random. Each play is short, and you play repeatedly to solve the anomalies ...... or rather to collect cards. It's something you can play regardless of the storyline!