When Ling Han had been in the Celestial Realm, he had killed over 100 Foreign Realm Celestial Kings through trickery in one fell swoop, obtaining astonishingly great military merits, and he had also redeemed uncountable Godly metal from the heavens, which would be sufficient to push the Devouring Metal to the level of Divine Metal.
Previously, when he had fled into the Foreign Realm, he had not managed to pay attention to the Divine Demon Sword. Furthermore, it had not been very urgent, either, and now that he had found some time, he finally recalled that it was time to upgrade this Divine Sword to the grade that it should have.
Because there was really too much Godly metal piled together, it was even larger than a planet. Thus, Ling Han was boosting the Divine Demon Sword inside the Black Tower. Otherwise, if he had taken out so much Godly metal, he really would have had to abandon this neutral zone as well.