its a special limited item that you use on 3rd form monsters to give them the other 2 abilities you skipped when evolving them.
there are 2 ways. 1 is a random greater blessing reward from completing a loop in infinite mode. The other requires you to build an Aurite Mine at your village and have 3 mons working at it. This will allow you to buy 1 radiant during your runs as a new option from aurite locations (its expensive tho)