and most of the time he actually fakes his smile, like they show us that time when he almost past away for the pain in his broken arm but tries desesperatly to stick to his usual smile
As I said before, he is actually a very serious and calculative person, but always tries to act like he is just devilish happy, like here:
His actual feeling vs what he shows.
I think he likes to be underestimated, like he focus all the attention on Sena and just acts as if the team couldn’t run without him when is actually Hiruma the one who is the most important, and to do this his actitude is very important. A lot of people look at him and they are like “lol you try to act so evil but your plays are basic” and then he sudenly thinks in a genious plan that totally crushes them because he is taking this more seriously that they think.
Mostly, for Hiruma, his smile is a weapon. At least the fake one.
Because he does have a true smile that we can see for time to time and that is actually less showy, is just an honest one
Something that I noticed thanks to my brother is how serious he is at the start of the series.
Like he jokes and puts evil smiles on but there are a lot of scenes with him just watching everybody with a serious face.
I remember that one time he was laughing really hard and my brother was like “wtf, he is laughing, thats so weird” he is not the most observative person but he’s got a point. I had noticed before that he was more serious at the part of the series when Musashi is gone.
The fact that Musashi leave is really important for the story because it changed Hiruma and Kurita overall.
As I said before, Hiruma likes to actually loose it and have fun, but he only truly does it with his closest friends (or alone), and, at first, those were only Kurita and Musashi.
The image above is actually him talking with Musashi.
What I’m trying to say here is that he was so afected at the start, that we barely see his real smile.