"The aura of blood slaughter was too thick at the time, making it hard to make a move."
Yu Nan gave a simple and very true reason. Although the sword spirit was benighted, its killing intent was growing more and more ferocious. If we disregarded losses and smashed the Xuan Huang Killing Sword, we would have had some certainty of success, but the resulting damage was not something Teacher and the others were willing to bear.
At that time, the other party proposed that he had a way to weaken the foundation of Xuan Huang to reduce losses, and also made an agreement with Teacher: once the Xuan Huang Killing Sword left its nest, Teacher would step in to strip the Xuan Huang sword spirit from the sword and destroy it. As for the demon Wu An captured by the Demon Manor Spirit Banner, he was also designated by the other party, meant specifically to deal with the aura of blood slaughter. Over this period of time, forcing the Xuan Huang Killing Sword to change its route also involved a hand from that person.
"The mastermind behind the scenes..."
Judging from the previous changes, Yu Nan's explanation had strong credibility, but Yu Ci would not listen to just one side and believe it completely. After all, he had absolved his own teacher of most of the responsibility, and the motive was far too obvious.
The so-called "mastermind" was a vague figure, but Yu Ci could roughly piece together such a picture:
At least eight years ago, the other party had already begun plotting, while keeping the matter strictly secret and covering it up extremely well. Until he lured that second-generation disciple of the Siming Sect into the trap, drawing down the heavenly tribulation and weakening the Xuan Huang Killing Sword...