I always have a funeral for every youkai I killed.At their funeral, I would offer them the flower and pray for them.be cleansed and made pure,
we proclaim and request of the heavenly spirits of celestial realms, eight million divine spirits.in Tsukushi, Himuga, Tachibana, Odo and Awagi plain
purified with ablution,
and at that time brought into beingThe divine forces of purification.
That all the various defiling things, sins and impuritiesOn the high heavenly plain
divinely sit the god and goddess yin and yang forces
in blessing, as the imperial ancestor, Izanagi
Original Shinto prayers from here.
Translation by Stephen K. Hayes taken from here.
Full English translation of The Great Purification Norito Prayer based on the modern langauage is here.