Naruto: Pure Pathfinder!
These mystical beans, grown only in carefully hidden locations in the world, allow a being to recover a small part of expended chakra energy almost instanteously.
Each bean can restore X chakra points to the character, where X is equal to their caster level (the sum total of classes which grant chakra points).
Given their rarity and ability to turn the tide of a battle, the beans are quite expensive, weighing in at (insert cost here) per bean.
Eating a Senzu bean is a standard action (like drinking a potion) but does not provoke an attack of opportunity.