Inuyasha Chapter 343-345 Miroku's "Fiance" an "Error from the Past"
In the anime, Miroku had asked a 13 year old child to bare his children—while he hadn’t seemed to have been completely serious, it was still a very odd thing even to Sango and Inuyasha who grew up in that era.
However, the chapters that episode is based on doesn’t actually reveal the age of the girl named Shima nor does it illude to her being incredibly young. These chapters are actually about Sango's jealous towards Miroku's supposed "fling" or "past girlfriend". [Edit: I mixed up the chapters. In the episode I mention, Miroku actually asked an 11 year old to bare is children named Koharu. It is never suggested that he slept with her like Shima, but it's still incredibly gross for him to ask a tiny 11 year old that. And she WAS tiny in her flashbacks, he knew but he said that anyway.]
The only timeline we are given is that Miroku met Shima 2 years ago. Now, I and others in the manga refer to her as girl since she is clearly a teenager much like how Kagome is referred to by girl. I do not have access to the Japanese version, but I am assuming that they used the pronoun "onago" for her which apparently refers to girls under the age of 20 or perhaps 19. I would like to double check with my Japanese friend, but I don't have the Japanese version. However, as the chapter goes on it becomes very very clear that Shima was a teenager 2 year ago and that she wasn't obscenely young in that time like she was portrayed in the anime.
Notice how Kagome and Sango react to Miroku upon hearing this compared to how they physically recoiled in the anime. Here is just as he always was: a womanizer but not a man who preyed on a little girl. Miroku is apparently 18 in present day and would have been 16 2 years prior, but even in the anime, it was creepy for him to have said such a thing to a young girl. Here there is no such reaction.
Sango acts very aggressive towards Miroku throughout the chapter because she expresses jealousy over his "past girlfriend" showing up. She expresses this explicitly by the end. At this point, the parents of Shima and trying to get Miroku to marry Shima hense Sango's displeasure since Miroku had started going "steady" with her some chapters earlier and had even promised to marry each other (He had yet to give up his womanizing completely however, so their relationship is still on the rocks. Yes, this is one of my gripes with his character and their relationship, but this is focussing on whether he had canonically hit on a 13 year old child).
Moving on, the demon bargain with the father for healing Shima (apparently but it's not clear if he had did anything but make do on the promises of the father to "give anything" for his daughter's health) had been on the terms that Shima was a pure girl to become his bride. The father suggest marriage will stop the demon's advanced but Miroku doesn’t agree that it would solve the problem.
To stop the demon's advances, Shima confesses to having had "joined" with Miroku 2 years ago that is to say that she is not "pure". Since she was obviously not wed and her insitence that she was not pure, it is clear that she confessed to having sex with him. This shocks the demon and infuriates Sango yet she hides her fury behind saying that it was a mistake of his back then something that she would have expected considering Miroku's history.
To stop the demon's advances, Shima confesses to having had "joined" with Miroku 2 years ago that is to say that she is not "pure". Since she was obviously not wed and her insitence that she was not pure, it is clear that she confessed to having sex with him. This shocks the demon and infuriates Sango yet she hides her fury behind saying that it was a mistake of his back then something that she would have expected considering Miroku's
However, as it turns out, that was a lie on Shima's part as an attempt to get out of marrying the demon. Buuut as it also turns out, Miroku just couldn't remember if he had had sex with her despite trying to play it off as expecting Sango to trust him.
Now it is abundantly clear that Miroku has in fact slept with multiple girls in the past since one can't just forget if they are a virgin or not, he just couldn't remember if he did in fact sleep with Shima.
I can feel the presence of weirdos coming to say 13 is old enough to have sex, but this is wrong for so many reasons that I don't even have the energy to describe right now. (Btw, most places in Japan the age of consent is 16-18 except for two islands which are uninhabited https://www.worldatlas.com/articles/what-is-the-age-of-consent-in-japan.html) I will however describe why it seems like Shima was at least Kagome's age those 2 year prior meaning that she is about Miroku's age during this chapter.
The reason I speculate that she is ~17/18 and was ~15/16 is because Kagome is 16 and a modern girl. Had Shima been younger and implied to have been significantly younger than 16, Kagome would have likely expressed shock as she did in the anime [edit: rather in chapter 147 about Koharu, so obviously Shima is considered old enough by Kagome unlike Koharu]. This is the same Kagome whom Rumiko didn't even have kiss Inuyasha until she returned after she graduated. There isn't anything in the chapters that make Shima seem incredibly young like she was in the anime, at least from what I can see from an English translation. I also doubt that the Japanese version refers to Shima as being such a young girl as she was in the anime since the context is that of jealously on Sango's part rather than disgust over bedding such a young girl.
So that's my analysis of that...but there's one little tidbit I'd like to point out 😏 Chapter 343 is called "Fiance" and it actually opens with Sesshomaru and Kagura. This chapter is actually when Rin proclaims that Kagura must be in love with Sesshomaru. Just a little tidbit that was an interesting coincidence considering this this is the first time Rin makes such an observation about Kagura. Quite an interesting chapter name for Rumiko to have Rin make that remark.
Also Kagura is very clearly trying to get Sesshomaru to help her kill Naraku for her freedom which is why Jaken lements over how simply minded she is, but as we would find out much later, Kagura did in fact have affection for Sesshomaru and he did of her during her passing.