Back then, when Zheng Yuanzi discovered the Thunder Spirit Beast, it wasn't as though he had never thought of swallowing its other "half-body." But at that time, his strength was feeble, and the Thunder Spirit Beast had already developed consciousness. Had he tried to forcefully fuse with them, it would have surely put up a desperate resistance, likely resulting in mutual destruction.
Being merely a beast, he didn't pay it much mind, figuring that letting it grow somewhat stronger would also be beneficial.
Sooner or later, he intended to harvest the Thunder Spirit Beast. However, by the time he had grown strong enough, Old Turtle had sealed the Thunder Spirit Beast away and vanished without a trace. He never in his wildest dreams expected such an outcome; he had looked down on the Thunder Spirit Beast, only to end up being the one swallowed.
Chapter 939