Rai possesses an earring on his left ear which shaped like a cross. These earrings are actually seals that withhold the outflow of his tremendous power which otherwise, would have been too much for his body to take on because he was using so much power before. Releasing the earring lets Rai to use how much power he wants to use.
From the Previous LordEdit
The Previous Lord gifted Rai with the two earrings laid on velvet in a small case as a birthday present. He made them personally for Rai. Rai kept one of the pair within the box in his mansion and wore the other one. Each earring is made of pristine silver and is shaped like a cross with tetrahedral edges. When one was removed by Rai in the previous Lord's shrine while dueling Raskreia, it disappeared into thin air after a long period of use. Rai undid his seal once again after awakening from his short hibernation.
In order to reinforce the enhancements designed to stop Rai's powers from seeping, Frankenstein gifted his master a piece earring similar to those crafted by the previous Lord. It is similarly cross-shaped with tetrahedral edges but rather than silver, it is shiny black with only one glistening gem studded in the center. This color stems from the dark power within as it is forged using the Dark Spear. Its attributes are closer to the earrings crafted by the previous Lord and Rai himself has verified that it is more potent than the ring Frankenstein gave him before. (Chapter 286) Rai has one strong complain which makes the earring unsuitable to his taste - the color.