Sesshōmaru, born of a great demon bloodline, possesses the perfect power that many demons desire. Because of this he is always composed and confident in his power.
His air of aloofness and indifference is a product of dignity that only one of such rare demon power may possess. Sesshōmaru is more or less emotionless, only anger, annoyance, and dissatisfaction showing on his face. Because both his heart and body are so strong, he had no desire whatsoever for the Shikon Jewel. He had absolute confidence in his power, so he did not need the Shikon Jewel and doesn't have to conspire with allies. Sesshōmaru even responded sarcastically towards Naraku, who had assumed an air of impudence due to his increased demon power. In battle he judged his enemy's power level and attacked with the minimum power necessary. He dealt with his enemies after determining their power. Once he had realized their weak point, their attacks were futile.
Sesshōmaru is obsessively proud of his father the Inu no Taishō, of whom the whole demon world was in awe. Because he respects his bloodline so much, he despises Inuyasha as well as Inuyasha's human mother Izayoi. He insults Naraku, who tried to take advantage of Sesshōmaru's power. All that his father left him was a dull sword that wouldn't cut anything. Anger welled up in his heart for not being able to use Tenseiga, which was left by his father, whom he highly respects. Sesshōmaru held resentment towards his father for having left Tessaiga to Inuyasha, whose power was weaker than his own. However, over time, Sesshōmaru comes to grasp why his father gave him Tenseiga and lets go of his disgust towards his half-brother, even showing concern for him in rare moments. He was also secretly angry that Naraku, who was assembled by demons far lower in level than Sesshōmaru, used abusive language and disrespect towards him. Sesshōmaru had stated that he seeks to only fight the strongest beings alive and how he had wanted to fight his father and defeat him.
Sesshōmaru felt nothing for others, sneering and dismissing humane feelings. Anyone in his way is an enemy whom he will exterminate without hesitation. He does not hold back his power, even against women. He rationalizes that all his prey is the same and defeats them accordingly. For one with such pride in his power, cooperation is proof of weakness and being alone is a condition for the strong. Once he judges someone as an obstacle, he is quick to kill without hesitation.
He used to feel nothing for anyone, but meeting various people, such as the ever-changing Inuyasha, Naraku with his numerous proposals, and all-alone Rin had brought change to his heart. After he saved Rin and became a true owner of Tenseiga, he started to show feelings behind his heartless and cruel words. He stopped the demonic Inuyasha's wildness by controlling his power and he looked at him like an older brother reprimanding a younger brother, though claimed he would kill Inuyasha despite his actions showing the opposite. He even refrained from killing Kohaku when he could easily do so, when he looked in his eyes and saw emptiness and that he had given up everything.
Sesshōmaru has a very inquiring mind when there is something he cares about, but at the same time, he had almost no tenacity of purpose. If he becomes interested in something else, he will arbitrarily turn his back on what he's doing, even during battle. Just like his fighting style, he is quick to make decisions and act on then immediately.
The encounter with Rin awakened him as the true user of Tenseiga. The smile and fleeting life of this young girl who tried to save him caused Sesshōmaru to change for the first time. The will of his father, who cared for humans, has finally been passed to his oldest son. Sesshōmaru used to leave anything behind that might bind him but he has slowly but surely changed. Sesshōmaru genuinely cares about Rin and Jaken and while he rarely shows it, he does appreciate their loyalty. Sesshōmaru originally held much contempt towards protecting the weak, seeing it as a waste of time and ridiculous. Unlike the Inu no Taishō and Inuyasha, Sesshōmaru has trouble admitting he had people to protect (Rin and Jaken) and out of pride, would never admit that he does, asSword of An Honorable Ruler showed. Another trait of Sesshōmaru is one he shares with his younger brother. Both have tempers and are very easy to annoy (Inuyasha being loud in his anger, Sesshōmaru being subtle) as he has been known to hit Jaken when he says something that displeases him, similar to how Inuyasha is with Shippō.