Isn't this redundant?
Facing him with his perfect parasitic abilities, there was no need for Flandre to give him the blending liquid. At most, she would present him a 'wax sealed stamp'.
Unless this younger version of Flandre had no idea about his parasitic ability in the first place.
Thus, the two Flandres were not the same person at all!
With that thought, Lin Xun immediately set out for the ancient nest.
For safety's sake, he didn't go straight to the third floor where Flandre was. Instead, he first went to the second floor of the nest, which was a resurrection point, and teleported back to the birthplace, the monastery.
Once the confession room of the abbey was set as the resurrection point, he teleported back.
This way, even if his conjecture was wrong, leading to a fall-out with Flandre, he wouldn't keep dying repeatedly in the ancient nest, waiting to be preyed on by this super BOSS.