I'd like to identify this anime TV show or movie. I saw it about 6 years ago, late night, on Cartoon Network/Adult Swim/Toonami/Boomerang, in English language.
At the beginning of the show there was these monsters that were attacking a village or a town and then this girl gave him a gem that was on her forehead. The gem bonded to him and then he fled away from the destruction. There was about 5 to 8 people that had these "gems" and they were teaching him how to use and how to transform into these bio monsters.
There were different elements: one guy had the water element. But the kid had a special type of "gem" that nobody knew what his powers or limit was. The crystal or gem was blue.