A plot twist could be that the pregnancy was a result of some sort of magical interference. Maybe a powerful enemy cast a spell on them that made Kagome pregnant, and they have to find a way to break the spell without harming the baby. Or, it could be that Kagome's pregnancy reveals secrets about her family's past that she never knew. This could lead to her having to make difficult choices about whether to continue with the pregnancy or not, all while Bankotsu is trying to support her through this difficult time.
The plot could twist when they find out that Kagome's pregnancy is progressing at an abnormally fast rate. This could be due to her connection to the feudal era and the different time - related magic there. It might also be that the baby has some special powers that are causing this rapid development. Additionally, there could be a plot twist where Koga's pack has different reactions to the pregnancy. Some might see it as a sign of weakness, while others see it as a new beginning for the pack.
One possible plot twist could be that the pregnancy is a result of some dark magic manipulation by Naraku. Maybe he had a hidden agenda all along and used some ancient spell to impregnate Kagome. This would lead to a great internal conflict within Kagome as she has to deal with being pregnant with the child of her enemy.
One possible plot twist could be that Kagome's pregnancy is not a normal one. Maybe there are some demonic elements involved due to Inuyasha's half - demon nature. For example, the baby might have some special powers that are not typical for a human - demon hybrid. This could lead to various challenges as they try to protect the unborn child from those who might want to use its power for their own gain.
One possible plot could be that Bankotsu and Kagome initially face many challenges in their relationship due to their different backgrounds. Bankotsu, being from a more violent and rough past, has to learn to be gentle and nurturing. Kagome, on the other hand, has to help Bankotsu understand the modern values she brings. When they find out they are having a baby, they start to build a more stable home. Bankotsu might go on adventures to gather resources for the baby's future, while Kagome focuses on her pregnancy and preparing for the new life. The baby could also inherit unique powers from both of them, leading to an interesting story arc about protecting the baby from those who might want to use its powers.
In the fanfiction, Kagome could be drawn to a strange energy and find child Bankotsu in a forest. He has been separated from his group. Kagome, using her powers, tries to heal a small wound he has. Bankotsu is both curious and a bit scared of her. This meeting could be the start of a series of events where Kagome unknowingly plants the seeds of either his redemption or his greater evil, as her kindness might be misinterpreted by Bankotsu as a sign of weakness or something to be exploited later on.
One possible plot twist could be that Lorelai initially tries to hide her pregnancy from her family and friends. She might be afraid of their reactions, especially if she's not in a stable situation. For example, if she's a young woman still in school or just starting out in her career, the pregnancy could be a huge disruption.
Another idea is that Bankotsu gets injured and Kagome, with her kind heart, decides to nurse him back to health. During this time, they have long conversations about their different worlds. Bankotsu shares his tales of battle and Kagome tells him about her own world and the friends she has left behind. This leads to a mutual respect and a budding relationship.
It could be Naraku. Even though the focus is on Kagome and child Bankotsu, Naraku is always lurking in the shadows in the Inuyasha universe. He might see Kagome's interaction with Bankotsu as a threat to his plans and try to manipulate the situation to his advantage. He could try to turn Bankotsu against Kagome or use Kagome's distraction with Bankotsu to carry out some other evil deeds.
Their relationship would likely become more protective. Bankotsu would be more on guard, ensuring Kagome's safety during her pregnancy. He'd probably be more tender towards her too.
Bankotsu and Kagome fanfiction is interesting because it combines two very different characters. Bankotsu is often seen as a rough and tough warrior, while Kagome is more gentle and spiritual. A fanfiction could play on this contrast, for example, having Kagome's kindness soften Bankotsu's hard edges.