What's the name of the treasure brick that can add 12 to weapons in the BOSS area of magic domain?

Equipment or weapons+1 to +3 (inclusive) can be added to +4 with Xinghuibao diamonds.

Equipment or weapons +4 to +8 (inclusive) can be added to +9 with Yuehuabao diamonds.

Equipment or weapons above +9 (inclusive) can be added to+12 with a magic diamond.

You can use the demon soul spar without using precious diamonds. That's a question of opportunity. Sometimes you give up without adding.