Hiel was ridiculed for having a weak crest and sent away to a remote island. When he grabbed an ice ...
Prince with an unknown crest - basically a profession except the PTB give you a symbol and make you figure the rest out for yourself - is banished to a barren reef where he discovers his crest is Cave King and he's really really really good at mining. Gets a surprising number of shipwrecked visitors who decide to hang around because MC is just that nice, discovers ancient ruins, grows Yggdrasil in his backyard, defeats a leviathan, and has tons of wacky underground adventures.