Sword master is too straight laced.
Viper guy seems too simpleminded to do it.
Paladin seems way too obvious for a twist ending.
I think it's someone else.
Curses are written on C++? That's awfully specific and makes me ask stupid questions. Like...
What's written on C? On 1C? On C#? On Java? On Python? On Ruby? On Basic? On Pascal? etc.
Oh, thank god, MC isn't a completely deranged psychopath that would seduce a girl to manipulate her for his own goals. I think.
Also, MC is still in his idol group recruiter mode.
Honestly, the hero character defending MC even when he isn't present while sweet, feels kind of hollow. He didn't really do much when it truly mattered and unlike then he stands nothing to lose by doing it now. I won't be surprised if the rift between him and MC will widen the moment he realises...