What are these blue flames, and is there any treasure involving them?
Solution 1:
The blue flames are just aesthetic in this particular area. You can't do anything with them.
Solution 2:
These blue flames do not have any mechanical function. They are just ambiance.
They are a reference to Japanese folklore. Legend says, that souls of deceased people sometimes appear at night in form of Hitodama. Floating balls of fire in various unnatural colors.