Doujutsu

Doujutsu, as mentioned in the kekkei genkai, are ocular based bloodline limits of clans possessing special eyes that normally have their own sets of abilities unique to the wielders of the eyes. However, the eye techniques can usually be accessed by those who have retrieved an eye from one of the aforementioned wielders, and implanted them in place of their owns. Although, with the consequences of using the eyes and its techniques taking more chakra. Even just having the eye active at all times normally saps chakra of any users of the eye powers that have ad their eyes implanted artificially. Two such instances have been known of the sharingan, on multiple occassions and by various people, as well as the byakugan.