In addition to Gabriel's fondness for Serena, there was another reason that Kain allowed her to be so involved—the connections that she had through her family, and the wealth of information and resources she had access to because of it.
With his business now booming, and the income provided through his patent and work as an evolutionary planner, Kain had quite a lot of money—but there were many things that one couldn't buy just because they had the funds.
However, with the help of Serena, Kain was able to obtain quite a number of rare and expensive spiritual materials that he felt would be useful in more quickly promoting the "planet" in his star space, the golden dragon, and the tree of life.
Thanks to emptying out over 90% of his personal funds, the environment of the planet looked very different from the previous time he had entered.