Summary:

The sparks from his gem slow his racing thoughts as he opens the box. His breath catches. Inside is a soul gem, the biggest one he’s ever seen. It’s a simple gold band, but the gem is the ring, leaving no filler. Unlike Shane’s metal gold the soul gem gold looks like the sun itself spun into a single ring. It’s the biggest brightest soul he’s ever seen.

Mine. Shane thinks instinctively.

(or in a world where everyone has a gem that is the physical representation of their soul Shane finds out Ilya has been suppressing his and comes to the only logical conclusion: he has to steal Ilya's soul.)