Chainsaw Man's Yoru was always established to be a character with something up her sleeves. Most of her actions, however, unpredictable and erratic, did seem to have a certain undertone to them. Recently, her goals were revealed and if they are achieved, they could have serious implications. Given Death's impending arrival, she intends to defeat her sister, either through Denji or by weaponizing him.
Tied to this, a recent theory surfaced in the Chainsaw Man fandom which began to draw attention. It took into consideration Yoru's goals and imagined a scenario where she won. With that, the theory then went on to speculate what she might actually be after, following her defeating Death and standing in this new world (of sorts) with close to no one to oppose her.
Disclaimer: This article is speculative in nature.
Chainsaw Man: Yoru's plans may see her become an actual maternal figure

To begin with, in Chainsaw Man chapter 192, Yoru revealed what she wanted - the defeat of the Death Devil. This, according to her, could happen in one of two ways, i.e., she promised Denji physical intimacy if he beat Death, or else, should he fail, she would turn him into a weapon and do so herself. This seems fairly straightforward and incredibly (and nostalgically) manipulative.
But in chapter 195, Asa regains control and blurts out that Yoru was actually planning something even more terrible, quite unspeakable in fact. There would be little reason to doubt her given that the pair share thoughts and emotions. This is where the theory comes in to speculate what this might be. As per the hypothesis, Yoru might be looking to become a true mother.
To elaborate, consider that she wins and Death is defeated. Given Chainsaw Man's erasure powers, the concept of Death will be erased, effectively making humans and other living immortal. This would essentially create a new Hell on Earth - Devils running rampant, fearless, and humans scurrying in fear, unable to die to escape the chaos.

In the event that humans lose their lives, they would simply reincarnate (possibly), as Devils do. Thus, an endless cycle would be created. This Chainsaw Man theory further goes on to say that with time, humans and Devils might procreate, leading to the birth of a new entity, Hybrids of sorts. As odd as that would be, it cannot be ruled out in Tatsuki Fujimoto's chaotic world.
Furthermore, the hypothesis pushes the claim that Yoru doing all this would reinstate the Horsemen's contrasting goals - Control wanted freedom for humanity (a world free of death, suffering, etc.) and Famine wants to savor and enjoy things rather than consume them outright. On a similar plane, Yoru would be creating a world, highly chaotic, but showcasing a twisted love between humans and Devils.
If all this actually ends up happening, it may as well be Yoru who heads the food chain. Given the kind of strife that would ensue, Yoru's powers would only grow. Again, looking at the odd bond she shares with Asa (not Hybrid nor Fiend), she herself would be the strongest weapon, not to mention by that point she will have turned Chainsaw Man into one of her tools as well.
Final thoughts

This is yet another wild yet seemingly plausible theory that takes its place in the library of hypotheses formulated so far. When accounting for what Yoru has mentioned her goal is, this seems to make sense to a certain degree. However, with Asa revealing that her "partner" has something even darker in mind, a theory like this doesn't seem too far. After all, Yoru would thrive in the chaos.
But then again, there are a couple of points missing. For instance, how and what form would humans take when they reincarnate, or would the erasure of Death's concept mean Devils also become immortal and never return to Hell upon dying and simply wake back up? There are nuances to consider, but those aside, the theory doesn't seem too far-fetched, although quite wild.
Related links:
- Chainsaw Man chapter 195 highlights
- Does Fujimoto introduce the Death Devil in Chainsaw Man chapter 195? Explored
- The new Chainsaw Man character in chapter 195 might be a forgotten Horseman