This is Tenshiro's and his makumi's (Sword of grace) combined power form, called Kyōmei (Resonance).

Tenshiro's sword spirit is called Taiyō Doragon that means "Solar Dragon". In short Tenshiro calls her Tai. But during combat he uses her full name.
Together they form an unbreakable bond and in Resonance form they fuse together, carrying a name Tenryū no Taiyōfunka (Solar eruption of the Heavenly dragon) and taking a form of a light dragon who shines as bright as sun. Of course they can control the brightness but during the activation it's wise to cover eyes unless wants to become blind.
Tenshiro's sword takes a form of a saber which blade emits light and strong heat givign it ability to cut any tough objects. It's hilt has two golden ribbons attached to it and guard is made of strong carbon steel.

This image did not take me long to do which is a bit of suprise. Enjoy!