ko ▁uses ▁a ▁pair ▁of ▁cre atures ▁named ▁M ok ona ▁Mod oki ▁that ▁are ▁able ▁to ▁cross ▁world s . ▁Y ū ko ▁created ▁these ▁cre atures ▁alongside ▁the ▁sor cer er ▁C low ▁Re ed ▁in ▁anticip ation ▁for ▁the ▁series ' ▁events . ▁During ▁T sub asa ▁it ▁is ▁revealed ▁that ▁Y ū ko ▁was ▁once ▁going ▁to ▁die ▁but ▁C low ▁Re ed ▁accident ally ▁used ▁his ▁powers ▁to ▁free ze ▁time ▁for ▁her . ▁After ▁her ▁time ▁is ▁fro zen , ▁she ▁becomes ▁the ▁enemy ▁of ▁sor cer er ▁Fe i - W ang ▁Re ed , ▁who ▁controls ▁the ▁main ▁events ▁of ▁T sub asa : ▁Res er voir ▁Chron icle . ▁Near ▁the ▁end ▁of ▁T sub asa : ▁Res er voir ▁Chron icle , ▁Y ū ko ▁is ▁rev ived ▁by ▁Fe i - W ang ▁in ▁order ▁to ▁prove ▁his ▁superior ity ▁to ▁C low . ▁She ▁then ▁gives ▁up ▁her ▁life ▁as ▁the ▁price ▁for ▁Fe i - W ang ' s ▁two ▁cre ations , ▁S ya or an ▁and ▁Sak ura , ▁to ▁be ▁re born ▁as ▁normal ▁humans ▁in ▁compens ation ▁for ▁how , ▁because ▁of ▁her , ▁they ▁were ▁used ▁by ▁the ▁sor cer er . ▁ ▁Before ▁dying , ▁Y ū ko ▁finds ▁Wat anu ki ▁and ▁tells ▁him ▁her ▁wish ▁is ▁for ▁him ▁to ▁continue ▁existing . ▁Over ▁a ▁hundred ▁years ▁after ▁her ▁death ▁in ▁the ▁ending ▁of ▁x xx Hol ic , ▁Wat anu ki ▁own