Kaiki's parents have secrets. Even from him.
By extension, Kaiki's parents being strange is his own secret. He learned to lie and redirect his friends' interest, and their parents'. Yes, my mother knows sword forms. Her dad thought it'd be good for her posture. (He really has no idea if she even had a dad. Presuming, there.) No, you cannot sleep over. My father is too tired. (He's fine. His eyes are bleeding again is all.) Really, you think they look like each other? Huh, I never noticed. (Perhaps they were cousins. Forbidden love.)
He has long since guessed they used to be ninjas, no matter how good they are at playing samurai.
His mother is more of a tomboy than his father. She used to have long hair, almost as long as Father's, but one day she cut it short on her nape and then it was all bristled spikes. No one in the village commented. Kaiki knows why they didn't, because when he closes his eyes halfway and watches her through his eyelashes, he sees the same long ponytail, though at the edges it's all blurred. Neither of his parents offered any explanation, even though he knows they know he can see it.
Sometimes it feels as if they are tied together more through guilt than through love, but the bond nevertheless is absolute. Everything else pales beside it, even him. Oh, they care about him, and in their own ways they show it -- Father will sit with him and listen and never judge one bit, Mother will go with him through sword katas until he has them down. They'll never say "not now, I don't feel like it."
He tries not to ask for their time too often.
The only question about their past he asks is at Obon, old enough to wonder more, young and stupid enough not to have learned to shut up. He's sitting by the river in the dark, watching his mother let candle after candle float away, each in their little colored lantern-boat. It's a samurai tradition. Most families only send off five or ten at most, though, but his mother sends off thirty, forty at least. He used to like it. It looks pretty.
He asks, is it really one light per soul? and his father's blind eyes turn to him, and he replies, One per family. He doesn't say that they already look suspicious with so many dead-lanterns and there's no need to make it worse. Kaiki hears anyway.
To him they are Mother, Father, to them he is Kaiki, Samurai in training, their son, and he knows they'll never tell him the names they used to answer to, before he came.