One common theme is the forbidden love aspect. Since Kagome is often paired with Inuyasha in the original series, a relationship with Sesshomaru goes against the expected. Another theme is power dynamics, as Sesshomaru is a very powerful demon and Kagome has her own unique powers.
You can try fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. AO3 has a large collection of fanfics and a good tagging system to help you find Inuyasha Kagome x Sesshomaru stories. FanFiction.net also has a lot of content, though the quality may vary more.
Another fanfiction concept could be set in an alternate universe where they are all students in a school. Inuyasha might be the troublemaker, Kagome the studious one, and Sesshomaru the aloof and brilliant student. There could be a mystery at the school that they have to solve together, and through this, they form an unlikely friendship.
Sesshomaru is an enigma. In fanfiction, his cold exterior and his pride as a full - demon are prominent. He initially sees Inuyasha as a weak half - breed, but as the story progresses, he may come to respect Inuyasha's growth. His relationship with Kagome can also be an interesting aspect. Sometimes he's indifferent to her, but other times he might be intrigued by her powers and her ability to change Inuyasha.
In fanfiction, the relationships between Inuyasha, Sesshomaru and Kagome can be very diverse. Some fanfictions might focus on Inuyasha and Kagome's relationship, which is often a complex mix of love and adventure in the original series. Their relationship is full of bickering and mutual understanding. While Sesshomaru, being Inuyasha's brother, may be depicted in fanfiction as having a more aloof or even begrudging respect for Kagome. He might interact with her in unexpected ways, perhaps even having a slow - building friendship or an unusual alliance.
Perhaps Sesshomaru sees some value in Kagome. Maybe he realizes that she has certain powers or knowledge that could be useful to him in the future, so he decides to save her from Inuyasha.
Yes, there might be some fanfiction out there with such a plot. However, it's important to note that these often deviate from the original positive relationships in the Inuyasha series. Fanfiction can be a creative space where authors explore different, sometimes darker, storylines.
In the original Inuyasha series, it is highly unlikely. Sesshomaru has his own character arc and goals mainly centered around power and his own pride. Kagome is in love with Inuyasha. Their storylines don't really lead to a romantic connection between Sesshomaru and Kagome.
One popular theme is the idea of redemption. Sesshomaru, who is often seen as a cold and aloof character in the original, might be on a path of redemption in fanfiction, and Kagome could play a part in that. Another theme is the exploration of power dynamics. Inuyasha's half - demon status and Sesshomaru's full - demon power, along with Kagome's spiritual powers, create an interesting mix for writers to play with.
One common theme is the idea of 'opposites attract'. Sesshomaru is often portrayed as cold and aloof, while Kagome is warm and empathetic. Their different personalities coming together is a popular concept.