The seal of Cloudy Fang still has some time left.
Based on the original timeline, at least it should be after Coral joins the protagonist group, Inuyasha battles the Dragon Bone Spirit, and masters the Blast Stream Break technique, so it shouldn't be a major issue for another month or two... Gu Mo wasn't too worried, and besides, the seal can be reinforced further.
There's still plenty of time now.
In the original plot, this demon sword was able to run amok mainly because nobody in the modern world knew about it, or even recognized it, and naturally wouldn't know its true nature or potential dangers, nor were they aware that its seal was about to expire... No one cared, and no one renewed the seal, allowing the demon sword to unseal itself.
But Gu Mo, who knew everything, naturally wouldn't just watch such a thing happen.
