The Siren is a painting by John William Waterhouse. The painting depicts a siren sitting at the edge of a cliff, lyre in hand, staring down at a shipwrecked sailor floating in water, who in turn is staring up at her. The picture was painted in 1900 and is now part of a private collection.
https://en.wikipedia.org/wiki/The_Siren_(Waterhouse_painting)
In most media with sirens I've seen they turn monstrous before they feed. I've always felt like it would be much more disturbing if they didn't. This gives me some of those vibes. Awesome painting.
What might a non monstrous one do their victim? Eat them still? Or some cosmic unimaginable horror?
Yeah I picture it looking like cannibalism with a disturbing amount of glee. Personally I find the idea of this nearly human creature happily devouring flesh to be quite creepy.