One possible plot idea could be the exploration of how Mitsuri and Obanai deal with the impending arrival of their baby. Maybe they face challenges like preparing a safe home in their demon - slayer world. Another could be the reactions of their friends and comrades to the news.
There was no clear connection between Sanguine Red's novels," Tengen " and " Tengen 1 ", which could form an independent series. However, judging from the name, Tengen could be considered a follow-up to Tengen 1 because Tengen was usually used to refer to the first work in the series. However, this was not absolute, because the name connection did not necessarily mean that there was a direct causality between the works.
Their relationship might become more tender. Obanai, who is usually aloof, could become more protective of Mitsuri. Mitsuri, on the other hand, might rely more on Obanai for emotional and physical support.
They have a complex and somewhat ambiguous relationship. It's not straightforward love but a deep connection based on mutual understanding and shared experiences.