Kayanu was the former head of the assassin training unit of Nether Gate when the group was under the authority of the Falenan Royal Family. He was the person responsible for the training of Lyon and Sagiri and all their emotional and mental damage.
After Arshtat Falenas rose to the throne, she ordered that Nether Gate be disbanded. Rather than resist the order, Kayanu fled the country with Takefute, the commander of Nether Gate. The two eventually made their way to Nagarea where rumour has it that they have continued the organisation there.