It's a video game adaptation. The first Siren was a 2003 survival horror stealth video game from Keiichiro Toyama, the creator of Silent Hill. A sequel (Siren 2) appeared in 2006 alongside this movie adaptation... but although their setting (Yamajima Island) and monsters ("shibito") are related, they couldn't be more different underneath. The game sounds like a big ambitious Lovecraftian thing, while this film is small and narrow. At best, you could call it "loosely based" on the game.

THE GAME HAS... an ancient water deity called Mother, who's sending out avatars to prepare for her return to our world. If they open seven gates of the Underworld, they'll unleash her. The human characters see their own four-year-old selves, or turn into magic trees. There are unkillable shibito (near-zombies) and yamirei (albino slug-things). A key game mechanism is "sightjacking", in which the player sees through the eyes of a nearby shibito or human in order to learn where your enemies are and what they're doing. Unfortunately, your real body is immobile while you're sightjacking, so you might return to find yourself under attack, or even dead.

THE FILM HAS... has only one sightjacking scene, ish, and quite possibly no supernatural element at all. It depends on your interpretation of a twist towards the end.

As a slow-burning J-horror, I don't mind this movie. Some people might call it boring, but the island setting is mildly creepy and I like the horror mystery material. Our heroes are the Amamoto family: father Shinichi, daughter Yuki and much younger son Hideo. They've moved to Yamajima Island for Hideo's health, but it has mute-but-watching-you inhabitants who mostly aren't Japanese and might have their own religion. There's a local rule. "When you hear the siren, don't go outside." Even their new house needs a spring-clean... and is that blood on the wall?

This is a solid enough start. The revelations work. The horror material isn't particularly scary, but I like the atmosphere. The final twist isn't particularly original, but it's a bit of a genre shift.

Unfortunately, the film has almost no characters. It has dialogue that's being said by people, but that's not the same thing. Actual characterisation is minimal and you could cut-and-paste most of these people with each other. Some of those character decisions are serving the final twist (I'll avoid spoilers), but...

1. YUKI AMAMOTO (Yui Ichikawa) = the main character, but she's opaque. Her father's distant and her brother's mute. This isn't a character-driven film. It's more about Yamajima Island and its mysteries, with Yuki being mostly a sort of audience analogue fulcrum in the middle of it. She's not unlike the player character in a game, i.e. a generic explorer.

2. HIDEO AMAMOTO (Jun Nishiyama) = a walking McGuffin who never speaks. He's a child actor. The prodution team had no intention of entrusting any dramatic weight to him. Once he nods and once he sings, but that's it. His role is to be a semi-animate object that Yuki wants to protect and help get better.

3. SHINICHI AMAMOTO (Leo Morimoto) = is a background presence. He brings his children to the island, then drops out of sight and leaves his daughter Yuki to carry the movie. (She doesn't, to be honest.) He's a writer and that's almost all I can tell you about him. Later on, the film uses him in a non-character-based way, though.

...and that's it. A couple of locals can actually talk Japanese. There's a nice doctor and a nice neighbour. Basically, though, this is a video game adaptation that's focused on reproducing something akin to the game experience without really making it character-based. I wouldn't even really call the film frightening. Its horror is understated and more about atmosphere and setting. It certainly doesn't recreate that tension that the best horror games can wring from you. Nonetheless, I did sort of like the film. It's not boring, but instead a slow burn.

Its characters are placeholders, though.