Ryūkon no Gi (竜魂の儀)

The Dragon Soul Rite Tsukibito have the innate ability to summon a dragon from their soul. It was made as a workaround by the First Tsukibito who couldn't turn into a full one. This dragon acts as a soul companion, following and listening to the user. It is fully unique t the user so 2 cannot share the same dragon (unless they occupy the same body). The way to activate the Rite is to pull out a piece of yourself as a catalyst. The piece can differ from person-to-person (Hajime pulls out a strand of hair, Shirou pulls out one of his scales). They can also summon specific parts of their dragon, like the head alone for a bite or its paw.