19(Demon Slayer)

An Au where Shinobu during a mission was cut in her lower belly and it was deep and big enough to damage her uterus and make her unable to have children.

Shinobu never thought about having kids but even if she planned to, she could always fall back into finding an omega or female beta instead of a male alpha or beta like Kanae always wished for her(in this au, their second gender presentation happens when they turn 18 but some give already hints to which will be their second gender before and people can present sooner or later due to trauma...also, while Shinobu never hide that she was an alpha, most people are oblivious to it) so while she thanked her fellow slayers when their gave her their condolences she didn't really care about having lost that ability especially as while Kanae dreamed of Shinobu giving birth to her own children, Shinobu was never found of imagining herself giving birth.

But imagine her shock when during a mission with Giyuu, she finds herself affected by a demon's powerful aphrodisiac and while she normally got an antidote for almost everything this time the demon's aphrodisiac had been much stronger then expected and the antidote Shinobu had only slowed its effects. Shinobu was already thinking of what she could do but unexpectedly Giyuu offered himself to help her satiate her need when she couldn't handle it as she worked on a stronger antidote.

While knowing that Giyuu was an omega, Shinobu was surprised by the offer since she was one of the rare people to know that Giyuu hadn't been with anyone since he lost his almost mate in the Final Selection but while she wanted to deny Giyuu's offer, she knew she had no choice as while having  a better control then most alphas, even she was affected by things like this.

So during a full week, Shinobu divided her time between producing an antidote when the aphrodisiac effects' calmed down and fucking Giyuu as much as her body needed.

Once Shinobu had the antidote and took it, the duo waited a day before making their way back to the Butterfly Mansion and then send a letter to Oyakata about how the mission went.

Neither planned to talk about that week ever again but the week spent together, gave fruits(if you want it to be twins or more instead of just one) which Giyuu found out when the boy he saved and spared his demon sister told him to be careful taking in account his situation. Giyuu had been confused and asked the boy to explain to which Tanjiro said that Giyuu smelled exactly like his mother did when she had been pregnant with his siblings. This shocked Giyuu but he quickly sent the two siblings to Urokodaki and make haste to the Butterfly Mansion to inform Shinobu of this and have her verify if this was true.

Both Shinobu and Giyuu were shocked when she made the test and the results came back as positive, neither of them ever planned to have children but it seemed like the universe  choose to give them children anyway.

They were unsure of what to do but one thing was clear from the beginning, neither wanted to abort the child so they took a week to think of what to do and in the end they decided to have the child and raise them together and if they ever ended up dating or mating, it was up to their future selves.

Shinobu requested a meeting with Oyakata where he was informed of what happened and gave Giyuu at least two years of vacations(if he wanted more or to give up being a demon slayer, it would be up to him) while Oyakata would lie to the other hashiras by saying Giyuu had been sent on a mission that would take a long time and limited his contact with others.

Giyuu had to think of a place to stay during his pregnancy and while he knew Shinobu would find a way to have him stay at Butterfly Mansion he knew that would cause too many troubles and decided that maybe it was time to see his master again and that by his master side he would always be protected even if demons found them.

Of course this made Giyuu have to tell Shinobu about the Kamado siblings and that Oyakata already knew about it too, Shinobu wasn't too happy about it but seeing that Nezuko did not attack Giyuu until he attacked Tanjiro she would let it go but requested ti have the chance to meet them to make sure Giyuu would be safe with them and so she knew the way to Urokodaki's home for when she wanted to visit him or have an appointment.

Everything went well, Shinobu took a bit of Nezuko's blood to try and find a way to help her but also that she may find a way to kill Douma that didn't involve killing herself too since she may have been willingly to do it before but now she would have her own kid and she did not wish to abandon her child, and Giyuu gave birth to healthy child which was named after the two people Giyuu and Shinobu loved the most and lost.

Giyuu returned to duty a year after he gave birth to his child and thankfully he met a lowermoon as he returned so he could lie to his fellow hashiras by saying that his mission was to deal and kill said lowermoon.

No one in the Demon Slayer Corps knew about Giyuu and Shinobu's child(except Ubuyashiki family, Urokodoki and the Kamado siblings) and the duo planned to keep it like that until the day of the trial where Urokodaki had been unable to take care of the child for some reason and had to trust it to a kakushi to take the child to Giyuu and/or Shinobu who had been at the moment listening to their fellow hashiras(and tryingt control their instincts in Giyuu's case since he saw the Kamado siblings as pups and seeing adults threathen little pups made his instincts stand up) when just as Sanemi stopped stabbing Nezuko and Oyakata arrived, the kakushi truste dby Urokodaki entered the place in panic with a crying baby in arms.

Giyuu just had to hear his child cry before hi moved as fast as he could to pick them up and calm them as Shinobu slowly walked towards them and questioned the kakushi about what the child was doing with them.

How anything else goes from here, including reactions, if ShinoGiyuu end up together or even if Shinobu and Giyuu survive(Shinobu the final battle and Giyuu the demon slayer mark's curse) is up to the writer.