The Devourer didn't advance directly towards the Demon Palace; as the Cleaner of the Sea of Lava, its work time is exceedingly long. The Devourer roamed back and forth in the Lava Sea, persistently clearing away the Soul Puppet variants blocking its path, allowing those inside its belly to enjoy a Lava Sea sightseeing tour. After a week, the lake within the Devourer's belly had expanded at least threefold. Only then did the Devourer complete its task. It swayed its tail, moving directly towards the core of the Demon Realm's profile.
...
The closer to the Demon Palace, the denser the Soul Puppet variants in the Lava Sea became, even showing forms of variants unseen before. However, in the face of the Devourer's massive size and absolute power, these Soul Puppet variants gained no advantage. A few daring variants that tried to challenge the Devourer disappeared instantly in the Devourer's breath.
Thus, another three days passed.
