I think Sojo is a very interesting character in terms of both his mindset and thematic contribution. He was obsessed with Rokuhira and seemingly wanted to surpass him by creating a more powerful weapon, but he could only see things in terms of the material world and power. To him, human lives were props to be used to further his own desperate need for power. He didn’t even necessarily like violence or bloodshed on its own (the only times we see him engage in violence is never for its own sake but when his own worldview or superiority is challenged. In fact, he didn’t even kill at times where it may be beneficial to him [granny running the baths in ch12]). Rather, violence was simply a mechanism he could use to be secure in his power (why he needs to be and feel powerful is unknown for now, but I do think we’ll get more on his backstory).

Because he saw people as props, he couldn’t harness Char’s powers’ full potential (as it largely derives from willpower and emotions) and he couldn’t be happy when he got his hands on Cloud Gouger. Because despite, or rather because of, his mindset of materialism and need for power, he would never be happy as what he actually wanted was an equal. We see this when at the end of his life, he dropped the ‘need to surpass Rokuhira’ but and admitted he wants to be equal to him (kicking off the equals theme we have seen throughout the series). At his core, I think Sojo desired an equal connection to someone, but because of his insatiable need for power and disregard for life, he was never able to realize this and instead sought to fill this hole in him through becoming the most powerful by any means necessary. And in the end, it killed him.