We know that evironment shapes character. Inuyasha IS clement, but he WAS once brutal and ruthless. Sesshomaru has always been cruel.
So, what had happened to both of them that made both of them ruthless? We already knew about Inuyasha's past: one that was full of afflictions. But how about Sesshomaru's? We can assume that Sesshomaru has never gone through hardships like Inuyasha, but we CAN'T say that there was NOTHING awry had happened to him in the past. If there weren't, he wouldn't be cruel and hating humans that much (Inuyasha ever said that, "I trust no one," before; and so did Sesshomaru).

Inuyasha wasn't accepted by both the human and the demon worlds, but Sesshomaru was by the demon world. Although Sesshomaru's situation wasn't as tragic as Inuyasha's, he wasn't abandoned and abased, but he was LONELY! Perhaps Sesshomaru's past was even more miserable than Inuyasha's.

I discovered that before Inuyasha met Kagome, he was just like Sesshomaru: Rejected by both the human and demon worlds, he simply doesn't want to show his weaknesses; he desired to become stronger, even at the expense of the others; he believed struggle would ensure survival; and in his eyes, humans are mere mortals. When Kagome came, she changed his whole life, just like Rin does to Sesshomaru.

I don't think Sesshomaru "wants to be loved" like Inuyasha does.

Sesshomaru just doesn't care what people might think about him; he just acts the way he does. All he wants is equanimity; or further, he may love solitude. He has lived for hundreds of years without a friend; why has he? And why isn't he bored? We can understand that he doesn't need others to survive. So, what is the purpose of his life and why does he continue living until now? He probably has some decisions/purpose now. Besides the purpose to kill Naraku, Sesshomaru has other purposes as well, such as to understand humans and to live peacefully with them.

In "Fukai Mori" (Deep Forest) song, I mentioned the lyric which says, "Seeking the light that we believe in," and these words definitely are delivered only to character Sesshomaru. Umm... I've been wondering... what is exactly "the light" that Sesshomaru is "seeking"? It could be the truth; it could be love; it could be future! Maybe he's seeking for a brighter future, the one that is free from solitude and affliction? Probably! This assumption of mine is verified by another line from a scene in the anime: "For someone as unremarkable as me, meeting you [Rin] is the best future of all."

Rin is the first person who awakes his conscience, but whether he will consider Rin as a lover one day is still a question that should be answered by Rumiko Takahashi. At the moment, the relationship between Sesshomaru and Rin merely is that of a father to a daughter, no more and no less. He wants to care a little bit more for Rin, to help his brother Inuyasha, and to cast a more careful eye on humans; yet with an extremely HIGH self- esteem, he doesn't do that. He merely doesn't want to show his weakness in front of people, especially in front of Inuyasha; he hates people to laugh at him, a demon who has always showed his disdain to humans. He's wearing a facade, hiding his true feelings from everyone. Even Inuyasha can't guess what is in his older brother's mind. Perhaps no one can understand Sesshomaru better than himself!

But no matter what, I believe that Sesshomaru will change, and he will understand what it means by LOVE.

But I also don't believe that Sesshomaru was NATURALLY cruel. Although from the beginning of the story, he destroys humans and demons aggressively, but it was the circumstances that obliged him to do so. Remember when Inuyasha was holding the Tetsusaiga and Sesshomaru was supposed to attack him, but he wouldn't have? I can say that he had a total advantage of killing Inuyasha (because Inuyasha was severely wounded), but he just left, and, I know well, he pretended to say that, "Inuyasha will swing the Tetsusaiga if [he] comes near."

Sesshomaru could have faced a past that was no better than Inuyasha's. I don't even know how I can describe further what I think by words.


Taken from: Mysterious Past (from my web)

I don't think of Sesshomaru as being someone cruel, look at humans, they hunt animals, kids even know how to squash bugs. Thats how Sesshomaru treated humans, as weak little bugs that bugged him.

Sesshomaru's goal has always been to become the strongest being to have ever existed. His goal would have been reached if he fought and defeated his father, known as the strongest being.
This so called act of cruelty displayed by Sesshomaru, I believe is something youkai inherit, through out ther series, how many full youkai have actually accepted humans as equals? Not many... most of them are evil... Taisho was one of the few to realize humans aren't all that bad, therefore having a change in heart. Currently, Sesshomaru must be experiencing the same thing through Rin, he's slowly become more tollerent of humans.
Inuyasha's cruelty towards humans was created from his past no doubt.

Sesshomaru was not being rejected by Youkai, when the invasion of the cats began (When inu was Sealed), Taisho and Sesshomaru lead an army to defend their country. Sesshomaru was a "well" respected as a leader and an extremely powerful force. I believe that Sesshomaru rejected more people than people rejected him.
The reason why he aint bored is b/c he still hasn't accomplished his goal in become the most powerful being. Naraku has not only become an annoyance to Sessh but also as a threat to his strength, another explaination can be that Sessh wants to be challenged, and obviously Inu cannot satisfy him.

The truth is that, even up till now, Sesshomaru's goal hasn't changed, even all thats happened to him, with Rin and all, his goal remains the same.

Yea, Sesshomaru isn't cruel now, but he WAS.

Both Sesshomaru's and Inuyasha's goals are to become stronger. In Movie 3, they even want to defeat their father to prove their strengths.

Inuyasha was rejected, but Sesshomaru wasn't. Sesshomaru is an introvert; he doesn't like people they therefore don't like him either. I think it's perhaps what makes him soft to an innocent child like Rin.