If you learned your first Japanese words from a show, you already know the problem. The characters shout, they drop particles, they call each other things you should never call a stranger. And yet an episode is forty minutes of real pronunciation, real rhythm and real emotion, which no textbook can give you.
What the extension does with an episode
Prima reads the subtitles as they roll and keeps a thirty-second buffer. When a line comes up that is just above your level, it pauses the video, opens the mic and asks you to say it. Then it lets the episode continue. When a scene ends, it asks one question about what happened, in Japanese, and grades the answer. Unknown words go to your Vocab Vault.
The register problem
Every line you shadow gets a label: casual, polite, or "only in this show". If you shadow a line in the casual form, Prima asks you for the polite form before the video resumes. By the end of a season you have a working sense of when desu belongs and when it makes you sound like a customer-service robot.
Two scenes on the map
The Scenario Map has a whole track for this. "Recap the last episode" trains the past tense on something you care about. "Casual or polite?" puts you at a convention with an older fan you admire, and the scene is about switching register as the conversation warms up. At Advanced, "Dub or sub?" is an argument about craft, not taste.
What it cannot do
It cannot make you a native speaker in a season, and it does not pretend to. It gives you a habit that fits around something you already do every week, with the cringe pointed out before it happens.