Thunder Stone

Thunder Stone comes in 2 variants :
 * 碧雷石 - Green Thunder Stone / Jade Thunder Stone
 * 蒼雷石 - Blue Thunder Stone / Sapphire Thunder Stone

Both Thunder Stones are always next to Ushi Gozen during the boss fight. Killing Ushi Gozen before the Thunder Stones will result in the raid quest battle to end, resulting in lesser number of possible /  /   obtained at the end of the quest.