Gilbert is a reserved, stoic and stern man who is stated to be unable to love anyone or be loved by someone else. Being a soldier, Gilbert was required to suppress his sentiments and pleasures, so he feels like he isn't allowed to show his genuine emotions. He feels like he cannot say what he wants to; he didn't have the right to nor does he think that he deserves to. Because of that, he thinks that his heart would be relieved if he earnestly put his thoughts into words. When he doesn't, however, feelings of guilt, regret, bitterness, frustration, anger, and sorrow would mix in his head. Gilbert is a stressed individual, and the frustration of things not going as he wanted would seethe within his head and burst out. He also has a bad habit of ignoring the pain of his conscience and pushing it to the back of his mind. However, when he says something he genuinely wants to say, it gives him a peculiar feeling likely caused by finally being able to muster out his most honest sentiments. He somehow feels that everything has been forgiven by confessing his feelings towards Violet.

Gilbert had an aptitude for the military, and he never felt any anxiety or fear when receiving promotions in the army. He thinks that God had bestowed him with a destiny that matched him perfectly. Gilbert has always felt like there was nothing he wanted to do nor a place he thought he could go to. He had come as far as he had by acting as expected of a child born into the noble Bougainvillea military family, hence he is rather envious of his friends who energetically speak about their dreams. Gilbert has very few things that he likes, and there’s a much bigger number of things that he detests. He simply doesn't say it, but he is not fond of his lifestyle. He states that although he does protect his country, he dislikes the world. He claims that the things he likes are his best friend Hodgins, his inevitably twisted family, and Violet.

Despite being a "pampered rich kid," he has a calm and warm personality with a real character to him. Sometimes, he does have a chilly and blunt personality though, especially when people question the obvious. Gilbert is also acquiescent, but that does not apply to everyone. However, he is also wise and has a strong sense of right and wrong and possesses real empathy. He is not merciless like his brother and is a compassionate and caring man who cherishes the ones he cares for, as he puts their safety above his own. Gilbert is deeply kind and carries strong morals with him, as he believes that his brother's actions in turning Violet into a weapon were sickening. This is why he offered Violet warmth and kindness, something that she had never experienced before.