Matamune gave his power to Yoh, who was then able to defeat the Oni which was terrorising Anna, although it uses up his remaining furyoku and meant that Matamune was unable to return to his normal form.
Matamune gave his power to Yoh. It uses up his remaining furyoku. Matamune was unable to return to his normal form. This was what it meant. Yoh was then able to defeat the Oni. This Oni was terrorising Anna.