Start by deciding her backstory. Maybe she was separated from her brothers at a young age and grew up in a different environment. This could influence her values and beliefs. Then, think about her relationships. Does she look up to one brother more than the other? How does she interact with other characters in the Inuyasha universe? Also, give her flaws. If she's too perfect, she won't be believable. Maybe she's a bit too trusting or has a short temper when it comes to protecting her family.
One plot idea could be that their little sister has a unique power that both Inuyasha and Sesshomaru don't fully understand. This power could attract various demons who either want to use it or destroy it. Another idea is that she gets lost in a different realm and has to find her way back while learning about her own abilities and the relationship between her brothers.
One popular 'little inuyasha and sesshomaru fanfiction' could be 'The Bond Beyond Rivalry'. In this fic, it explores the unexpected moments of understanding that develop between Inuyasha and Sesshomaru when they are in their younger forms. It delves into how their different personalities interact in a more innocent way compared to their adult selves.
One main theme is the exploration of family and rivalry. Since they are brothers, there's always that underlying family connection despite their rivalry. Fanfictions often play with this dynamic, showing how their relationship might have been different in their youth.
One idea could be to give the sister a unique power. For example, she could have the ability to control the elements, which would set her apart from Sesshomaru and Inuyasha. This power could also create interesting storylines as she might have to learn to control it.
In some cases, an antagonist could be a dark force or an ancient evil that has been awakened. This entity might target Inuyasha specifically because of his unique position as a half - demon. Sesshomaru then has to use all his skills and strength to fend off this threat and protect Inuyasha from this unknown and powerful foe.
You can also build a plot around her relationship with Sesshomaru. Maybe there is a rift between them that needs to be healed. She tries to do something to regain his trust or respect, but things keep going wrong. This internal family drama can be intertwined with external threats like demon battles.
In some fanfictions, Sesshomaru being Inuyasha's father can lead to really interesting plot developments. For example, it can create complex family dynamics. There might be stories where Sesshomaru has to come to terms with his new - found fatherhood and how it changes his relationship with Inuyasha, who he may have previously seen as an enemy or a rival. It also allows for exploring Inuyasha's feelings towards having a father figure like Sesshomaru, who is such a powerful and complex character in the Inuyasha universe.
Sesshomaru would raise the baby with a combination of discipline and protection. He would protect the baby from any threats, using his powerful abilities. At the same time, he would discipline the baby when it made mistakes, teaching it the ways of the demon world. Inuyasha, on the other hand, would add a more carefree and emotional touch to the parenting, creating a balance in the baby's upbringing.
In fanfiction, the baby could be the key to unlocking some long - lost secrets in the Inuyasha universe. Since Sesshomaru and Inuyasha have such complex histories and lineages, the baby might hold the answers to ancient prophecies. It could also have a special bond with the Jewel of Four Souls, perhaps having a unique way of controlling or protecting it that neither of its parents had. And of course, there would be all kinds of emotional drama as the two brothers - turned - co - parents deal with their new relationship.