When designing Overlord, Han Fei never thought that he could attach his soul to Overlord. Therefore, Han Fei didn't leave a battery groove-like slot for spiritual stones in Overlord.
It seemed that he needed to transform Overlord a little bit.
However, the first thing Han Fei had to do now was to continue deducing the Three Transformation Wondrous Book.
He pretended to be an Inferior Man-Fish and entered the Ten Thousand Demon Valley with the help of Yu Ji.
Therefore, Han Fei didn't think anyone would see through his real identity in the short term.
But now, when he heard that Yu Ji's master turned out to be one of the Eight Wings of Blue Feather, a powerful master of at least the level of a Law Enforcer, his heart did a flip.
He certainly needed to deduce the Void Fishing Art, but not now.