Acrium

It's true that he had gotten stronger and that his reserve of Soul force had seemed to increase unnaturally, but he had thought it was because Alan wanted to impress Erik and had to train and make even more potions than before.

He had never thought that he could have created this bond with Erik, besides at the time he was not even aware of this bond, so even if he had had doubts, he wouldn't have been able to find out about it.

But now thanks to his knowledge, he knew that this bond was as powerful or even more powerful than the mark of the Union because it allowed those who practiced dual cultivation to always become stronger and stronger.

And Erik's potential was that of a Warrior Spirit, so when he would reach the Stage 2, Alan would also probably undergo a transformation.