Is a nice girl, but much like our main character, she was born different, in that she has the unconscious power to cast glamor on everyone, guys become obsessed with her and pratically yanderes over time, being willing to screw over girls, and girls start to hate her, it just happens so much that the main character tries to avoid really interacting much with others as she can't stop it.
Though Al isn't affected by it, in fact, he heard from a friend his suspicions about what she can do and is planning to kill her for a ritual to have the glamor ability to be given to her so that everyone will love and pay attention to him rather than his sister, he does go through with it, but thankfully she only almost dies and starts living with the main character and Euphy who at first doesn't like her for obvious reasons and they finally manage to make her able to control her powers.
And yes, Al is aware that Euphy is innocent and he still went forth, he's a kid that was neglected as everyone paid more attention to his sister and she constantly shows she is smarter and better than him, in a way it's implied this social execution was him finally trying to emulate his sister for attention, only for her to crash down, steal his thunder and her and his parents deciding everything, they don't even ask him for his opinion or why he decided to annul his engagement, he was expecting someone to talk to him, but he got ignored.
Once he steals the heroine's magic, he gets more powerful and even tries to kill his sister, he is ultimately forgiven and his sister and parents feel sorry for how they treated him, and the two girls he hurt don't mind too, even though one was going to have her life ruined and he literally tried to kill the other, guy may have been neglected and unfavorably compared to his sister all his life, but that does not excuse attempted murder, he gets a brief spin-off managing his new land after he loses his royal position and finds a wolf girl, where he becomes happier and more relaxed in some ways.
