Interesting. Was the rain a one-time event or did it rain multiple times, killing more people as they inevitably aged past 15? I presume those over 15 that stayed indoors survived too, yeah?

EDIT: Additional questions and ideas.

If you go the zombie-like route, perhaps they could be nocturnal, in a way? Since rain is misty, cold, etc. and helps cool off the temperature, the zombies prefer cooler temperatures like those during nighttime. It'd make scavenging and what not harder during the day if there's a bunch of zombies more or less hibernating in an abandoned store.

Also, what types of characters are you looking for? People who were under 15 years of age at the time of the rain, but survived it somehow? Adults that survived it? A mix of both? I suppose I should ask where this RP would be based, too, to help with generating characters.