lmao you guys are whiners. only midwits seek to make everything materially legible and refuse to accept that sometimes, a little bit (or a lot) of make-believe sauce is needed on works of fiction, even "realist" ones like Kingdom: from the very start, what breed of human could perform supernatural physical feats that are exemplified in this manga?
furthermore, what kind of an idiot refuses the notion that Chinese hero stories in general are absolutely embellished with all kinds of weird things like cultivation, secret sage techniques, clans, obscure philosophies, etc? what's the difference between kyoukai's breath power and this chapter, anyway? categorically none.
finally, only the worst and most unthinking, consumptive kind of reader accepts a work of art at its face value---a good one interprets and reinterprets it as they want to and weaves its story with their own mythmaking, with their own stylized narratives. it is reasonable to say that the red stair and the conversation that was depicted in this chapter could be interpreted as, for example, kyoukai's brain creating her own imagery on how this resurrection techniques work---for all we know, the red stair could originally be something totally incomprehensible to human mind.
anyway, i'm out