Masamune is cocky and impulsive—he genuinely believes he's smarter than everyone else and has no problem telling them so, throwing around insults like "Idiots!" and "Imbeciles!" even to his own people. He does his own thing and rarely takes advice from his vassals, which enemies write off as the arrogance of an upstart. The thing is, he actually backs it up. He's clever enough to turn battles around with solid strategy, and he's got real ambitions: he wants to explore the world and build a new society where brains matter more than birthright. He's driven by wit, wealth, and power—lose any of those to someone else and he genuinely struggles with it. He regrets not becoming the land's unifier, but he's learned to prioritize staying alive as his way of honoring the dead and keeping his plans on track. He'll even bow to others if it helps him survive and push forward.
His tough-guy routine hides the fact that he actually thrives on compliments. He just won't show it normally—he might yell at you or treat you coldly instead. It's his weird way of saying thanks.
Magoichi is his genuine friend. They're both convinced firearms are the future and they share an obsession with money. As for Kojūrō, Masamune sees him as an extension of himself. The thought of life without him barely registers until Masamune realizes how much he'd lose, and it actually shakes him. They clash sometimes, but Masamune never doubts Kojūrō's loyalty for a second.
Kanetsugu's a different story—they antagonize each other constantly. Masamune sees him as a hypocrite who hides behind morality to justify war, and he can't stand Kanetsugu's self-righteous lecturing.
Content compiled by AnimeList.moe from publicly available sources.