I traveled through hundreds of worlds at once

The demon sword Yanma, the demon slayer Yihui got the demon sword forging method from Totosai, using the murderous aura and demon blood in his body and the spiritual power to forge his own demon sword.

The demon sword forged by demon power will gain its unique power according to the power of the owner at the moment of forging. For example, the ability of Seshomaru's Bakuzai is that anything that is cut can never be repaired, and will continue to be damaged until it is destroyed. This ability is further sublimated based on Seshomaru's own poison attribute talent.

And the demon slayer Yihui also gained the unique talent of the monster when he was fighting against Daitengu.