During her recovery from her Nosebleed in chapter 21, Shizuka says she prefers "Mr. Elephant" over "Mr. Giraffe". Does that mean she prefers Rentarou being limp as opposed to erect? Or is it the other way around?
It might actually go either way. Maybe "Mr. Giraffe" genuinely intimidated Shizuka, or maybe she's trying to bury her burgeoning Covert Pervert awakening.
If a person’s soulmate count is determined at birth, how are cases of Age-Gap Romance handled, considering one person in the pair hasn’t been born yet?
What sort of age gap would be significant in that case? If there is only an age gap of a few months, weeks or days, then this is also a situation where one person in the pair hasn't been born yet when the other person is born and this is technically the case with even a gap as small as a few minutes or seconds. It's likely that it is possible to either consider people that have yet to be born or assign someone who has already been born as a soulmate.
If the manga has No Fourth Wall to the point where Recursive Canon exists in this universe, how could Rentarou be the only person aware of the fact that an unloved soulmate would die?
In order for another person to be aware of the soulmate matter they’d need to know the manga and also encounter the other characters from the manga (provided they aren’t already inherently aware of the fourth wall and/or the manga’s premise) and that is presumably not the case for most of the characters. If someone hasn’t completely read all the chapters, then they might not recognize the later girlfriends even if they otherwise meet the conditions for awareness. Additionally, they’d specifically need to know the parts of the manga that actually explain the whole soulmate thing, so even girlfriends like Nano, Kusuri, Mei and Chiyo might not be aware of that due to plot reasons or Rentarou doing everything to stop them from finding out in order for them to not feel like as if they don’t have a choice in their relationship with Rentarou. Alternatively, they’ll later make a gag out of the harem or certain members of it already knowing about it from reading the manga despite Rentarou never telling them.
Ahko claims to be reading the manga in Chapter 172, so she probably knows.
How would Kusuri know if one of her drugs has fatal side effects if she regularly tests drugs on herself?
Death Is Cheap in this verse - maybe one of her ancestors stopped her spirit ascending into Heaven, like at the end of the bathhouse chapter.
