The truth behind their eyes

Y'see, in this world, slimes are unintelligent creatures, at least in their first forms, but they tend to cling to where they feel comfortable and don't make the same logical/illogical mental acts and hurdles that regular beings do. When slimes find something they like, it's not hard for them to grow attached or draw the line between hostile and friendly. Peach becoming a slime mother only gave her a higher intellect, not a lesser one, removing the human flaws in mental processes and keeping a clear and rational form of thought mixed in with some emotional actions. As for succubi, their existences require a quick bond that goes more than sexual ecstasy for greater results with their partners. This, coupled with the fact that they often have to make a run for it after their "meals", means that succubi have developed a yandere-like personality. It is imperative for succubi to be able to detach from their partners, but if they can stay with ideal or superb sexual partners, the succubus or succubi will do everything in their power to retain the company of the male. Thus, it isn't that these two women felt compelled to repay Gordon with sexual favours, it's merely a fact that their races form quick or immediate bonds that they can and/or will elevate while with the person, using them for sexual reproduction if the male is that exceptional or the situation is ideal/urgent enough.

Now, although basic slimes simply replicate in a form of mitosis and succubi use sperm as food, both Peach and Nautica need/want Gordon's baby batter so they can have his children. Since Peach is a slime mother, unless she wants to make mindless basic slimes, she needs human sperm to make humanoid slimes known as slime girls. As for Nautica, although succubi use sperm as food and a means to level up, they can selectively choose to use a creature's sperm for reproduction -unless it's an incubus, then the succubi has **** when it takes their sperm-. But as for their desire to reproduce in this current moment, rather than the how, the next logical step for these two races who've infested the world and thus require quick reproductive rituals and gestation, is to have Gordon's children.

Explaining just that, or something along those lines