One idea could be that their relationship starts as an unexpected alliance against a common enemy. As they spend more time together, they gradually develop feelings. When Kagome discovers she's pregnant, it could bring a new level of complexity to their relationship. Sesshomaru, being a proud demon, might initially struggle with the idea of impending fatherhood but then grow into a protective and loving partner.
Kagome would most likely be very angry. After all, being kidnapped against her will is a huge violation. She would probably yell at Sesshomaru and demand to be released immediately.
Love against all odds is also a frequent theme. Given their initial enmity or indifference towards each other, seeing them fall in love and become mates is a central aspect. Their relationship often has to overcome obstacles like other suitors, family expectations (in sesshomaru's case, perhaps his clan's view), and their own personal biases.
One common theme is the overcoming of differences. Sesshomaru is a demon and Kagome is a human, so there's often a story about how they bridge that gap. Another theme can be the protection aspect, with Sesshomaru protecting Kagome from various threats.
A possible plotline could be that Sesshomaru has to prove himself worthy to Kagome's family and friends. Since he has a reputation as a somewhat cold and aloof demon, this won't be easy. When Kagome gets pregnant, it adds more pressure. He has to show that he can be a reliable partner and father. Meanwhile, Kagome is trying to figure out how to combine her modern - world knowledge with the ways of the feudal era when it comes to raising a child.
One popular 'kagome and sesshomaru mate' fanfiction is 'A Bond Beyond Time'. It delves into the unique relationship that forms between them. The story is set in an alternate universe where they are forced to work together against a common enemy, and during this time, their feelings gradually change.
The theme of redemption can be found in many 'sesshomaru x kagome mate fanfiction'. Sesshomaru may have a dark past or actions that he needs to atone for, and Kagome's love and influence help him on that path. Another theme is the exploration of new powers. Their union may unlock new abilities for either or both of them. And of course, the theme of acceptance, as they have to accept each other completely, flaws and all, in order to have a successful relationship.
Another scenario could be that Sesshomaru gradually realizes that kidnapping Kagome to mate was a wrong move. As he spends time with her, he sees her kindness and intelligence, and he starts to develop a different kind of respect for her, rather than just seeing her as a potential mate. So he might let her go in the end.
One possible plotline could be a story of mutual respect and understanding. Kagome and Sesshomaru might start as reluctant allies, but over time, they come to appreciate each other's strengths. For example, Kagome's spiritual powers and Sesshomaru's combat abilities could be combined to fight a greater evil in the feudal era. Their relationship could grow as they learn from one another.
One great piece of 'sesshomaru x kagome mate fanfiction' is 'The Bond Beyond Time'. It beautifully weaves their relationship, exploring how Kagome's unique powers and kind heart draw Sesshomaru in. Another is 'Destined Mates', which delves into the cultural differences between them as they come to terms with their newfound bond. There are also many on fanfiction.net that are worth exploring.