"A boy awakes to see a girl's silhouette in the rain. He finds himself lost in a mysterious world."
That's how the trailer for JapanStudio's Rain (working title) opened up, followed by a gameplay demo showing off how you're an invisible boy who can only be seen while you're in the rain. Other invisible people will also get revealed by the rain in the world. When there's no rain, you're completely invisible and you can't be seen at all.
The demo video made it look like some kind of exploration puzzle adventure game, but it was hard to tell how the gameplay works between being invisible and silhouetted by the rain.
The trailer ends with "A story of an invisible world revealed by the rain."