It’s hard to walk around Japan without coming across the cuddly characters of “Chiikawa,” the web manga by the artist Nagano. They dangle from handbags, fill arcade claw machines and smile from Uniqlo T-shirts, making them among the most recognizable kawaii mascots of the current Reiwa Era.

It’s not surprising, then, that the franchise’s first feature-length film, “Chiikawa the Movie: The Secret of Mermaid Island,” has been a cinematic smash success since arriving in theaters on July 24. It earned ¥990 million on opening day — the seventh-biggest first day in Japanese box-office history — before reaching ¥2.24 billion by the end of the weekend. “Mermaid Island” is already shaping up to be one of the summer’s biggest hits.

What many didn’t expect from an animated summer-vacation movie was something closer to Dostoevsky than Hello Kitty, with stunned social media users describing it as “a horror movie.” They’re not entirely wrong.