I have one…kinda a big one that’s really a lot of smaller ones smashed together about Inuyasha and Sesshoumaru’s history/dynamic with each other. I’m not sure if it’s the kind of headcanon you’re looking for, but eh.
Here’s the full post, which is kinda half headcanon explanation and half watered-down fanfic thing.
And here’s a bit of a simpler bullet list of all the small headcanons it contains:
Full-blooded inu-youkai age at the same rate as humans through infancy and childhood, but once they hit puberty, the aging process gradually begins to slow down. They can live in their prime for well over a hundred years before showing signs of middle or old age.
Inuyasha (as well as other hanyou), on the other hand, ages at human rate throughout his life. However, he is still likely to outlive most humans his age because he has a stronger immune system and therefore is less likely to fall to sickness as soon as a human would.
Sesshoumaru was 7 years old at Inuyasha’s birth, 22 (but appeared ~14) when Inuyasha was sealed, and 72 (but appeared ~19) at the start of the series.
Sesshoumaru knew beforehand that he was going to have a little brother, but wasn’t aware said brother would be a hanyou until he met him. He was a little surprised, to say the least.
At first Sesshoumaru didn’t want anything to do with the hanyou. Over time, however, he grew used to the idea. By the time Inuyasha was just over a year old (14mo, to be exact), Sesshoumaru was actually pretty comfortable with his little half-brother.
The Inu no Taisho visits Inuyasha and Izayoi fairly regularly.
Because Izayoi is from a “ruined noble” family, their “village” does have a lot of space, but is rather small population-wise.
The Taisho fought the Ryuukotsusei to protect young Sesshoumaru, who had accidentally stumbled across the dragon-youkai’s layer whilst exploring the forest. Sesshoumaru feels that the wounds his father received are, therefore, his [Sesshoumaru’s] fault, which burdens him deeply.
The Taisho actually survived several months past the battle and almost made a full recovery. Most of his surface wounds were gone, save a few scars, but he still retained some nastily persistent internal wounds, which restricted his abilities.
At one point, an enraged, but relatively low-level youkai attacked Izayoi’s village. Instinctively, the Taisho raced off to save his wife and younger son. Sesshoumaru ran behind, insisting that his father not fight because his abilities were still crippled from the Ryuukotsusei battle.
The youkai that attacked the village should have been a piece of cake for the Taisho, but unfortunately, his limitations proved fatal. While he did defeat the attacker, the fight opened up some of his old wounds and overall exerted his body too far before it was ready. He managed to say a few words to Izayoi, Inuyasha, and Sesshoumaru before quietly passing away.
Sesshoumaru was distraught over losing his father. He still felt guilty about the fight with Ryuukotsusei, and now his father was dead because of those wounds. Sesshoumaru didn’t want to accept such an idea, so instead he tried to blame someone else: Inuyasha. Had Inuyasha and his human mother not lived in this village, or not existed at all, the Taisho never would’ve come after them, never would’ve over-exerted himself. In the eyes of a nine-year old emotional wreck, Inuyasha was the “cause” of the Taisho’s death. This is the root cause of Sesshoumaru’s hatred/bitterness towards Inuyasha at the beginning of the series. This bitterness grew to include not only Inuyasha, but also humans and hanyou in general.
Inuyasha was 2 years old at his father’s passing and 6 years old at his mother’s.
Izayoi died of disease. She fought the sickness for about a year before her death.
After his mother’s death, Inuyasha fled the village. In the forest, he met Sesshoumaru for the first time since the Taisho’s death. Sesshoumaru, needless to say, was still bitter and treated his brother like crap. Inuyasha eventually learned to avoid him. This is the reason Inuyasha is so bitter towards Sesshoumaru at the beginning of the series.
In-Series Headcanon (mainly a bridge between the pre- and post-series headcanons)
Obviously, Rin is the one who helped Sesshoumaru open his heart back up to humans.
During the series, Sesshoumaru never viewed Rin in a romantic way (good golly, she was just a child!), nor did he really ever view her as a daughter. Though he did grow to care for her immensely, he thought of her more as a ward to guard and protect than a lover or family member.
Though still far from being best friends, by the end of the series, Inuyasha and Sesshoumaru tolerated each other.
As Rin grew older and entered her teen years she began to develop a crush on her former guardian. She nursed these feelings for a while and began to seek out Sesshoumaru’s company more often. I don’t have full details for this part of their relationship (and probably never will), but around the age of 16, Rin somehow managed to convince Sesshoumaru to “do it” with her.
Rin later gave birth to a half-youkai daughter she named Mikomi. Sesshoumaru wasn’t aware of the child’s existence until after her birth. (See here to learn more about this OC. I mention her here only because she is integral to the end of my version of Sesshoumaru’s arc.)
Though Sesshoumaru and Rin do not stay together as a couple, Rin and Mikomi complete the healing of Sesshoumaru’s bitterness towards humans and hanyou. He eventually makes amends of sorts with Inuyasha. Needless to say, both brothers have matured remarkably since their initial conflicts.
Just throwing this in because I think it’s funny–Sesshoumaru, on occasion, has even awkwardly “lowered” himself to asking Inuyasha, who has several children, for parenting advice and help on understanding hanyou. (These conversations would be so awkward, haha. I should draw one sometime. XD)
