Kokushibo Blood can be earned after defeating Kokushibo in the Infinity castle, the last mission of the Slayer Storyline. When used by a Hybrid player, gives you Kokushibo's six eyes as a cosmetic. Furthermore, this item is not droppable due to being a boss drop. (The drop rate of the Kokushibo blood dropping is 25% chance Infinity castles.)
When changing your appearance at Peaker's barber shop, DO NOT change your eye type, as this will remove the effects of the potion. You can still change the colors though.
The six eyes that are given by drinking Kokushibo's blood.
Note: This change gives no buffs and is purely cosmetic.