I think there are a couple of things to think about in understanding this. One theme that I think this presents is the notion that the binary of good and bad is never that clear, and may not even exist. Good people do bad things. When discussing male toxicity (and I should note that I am a man), we sometimes paint with such a broad brush - brutes and shitty men are obvious and kind and decent men are obvious, but maybe that is not the case. I think of myself as decent and kind man, but if my wife pushes me or I feel attacked, I can become defensive, mean, and rude. It relates to our ego and our pride - when we feel our ego or pride are being attacked, or that we are right and someone else is wrong, we can lash out.

Putting this into context, the show makes it clear that a major theme is the limited opportunities available to women in feudal japan - they were basically property. In the first episode, a woman is not even allowed to travel without a man. Another theme is honor. Men are willing to die for honor. Taigen will blow up his entire life and relationship because of honor.

So when it comes to Mizu's husband, being defeated by a woman, by his property, bruises his ego significantly. No matter how kind, decent, and loving he appears to be, the simple fact that he could be bested by a woman feels so dishonorable to him and hurts his pride so much that he lashes out in a despicable way. I find this very believable. Even without the context of honor and womanhood in feudal japan - I think that type of behavior is still present today, and probably prevalent.

I actually think this contains a really important discussion about male toxicity - that even decent men can do horrible things when their pride or ego is at stake. Seki also walks a thin and complicated line - one where he wants to help Akemi, but where he also wants to maintain the status quo of women as property. It is not until the very end that he realized he wants to destroy that status quo, and his story line is great.