Justin Shamal is a character from the anime and manhwa Why Raeliana Ended Up at the Duke's Mansion. He is a young nobleman who holds the prestigious position of captain of the royal guard, a role that places him at the heart of the kingdom's political and social circles. As a member of the influential Shamal family, he is the son of a powerful marquis. There is some conflicting information regarding his family position, with some sources identifying him as the older brother of Vivian Shamal and others describing him as the younger sibling. Regardless of the birth order, his connection to Vivian is a significant part of his identity, placing him in the middle of the complex dynamics involving his family's ambitions.

In terms of appearance, Justin is recognized for his refined features, blonde hair, and yellow eyes, and he is consistently described as handsome and attractive. His personality is characterized by a captivating and charismatic nature. He typically projects a relaxed, carefree, and friendly demeanor, often greeting challenges and even his father's criticism with an easy smile and a seemingly carefree attitude. However, this laid-back exterior belies a deep sense of responsibility and seriousness when it comes to his duties as a knight and commander. He is respected for his innate leadership, bravery, and unwavering loyalty.

Within the story, Justin serves multiple roles. As the captain of the royal guard, he holds a fundamental position close to the royal family, responsible for the defense of the realm and possessing a keen strategic sense. He is also a primary romantic rival to the male protagonist, Duke Noah Volstaire Wynknight. Justin develops genuine feelings for Raeliana McMillan, the protagonist, and becomes another potential love interest for her, creating a love triangle that complicates her survival plan. This rivalry is deepened by a long-standing tension between him and Noah, as the two men are leaders of opposing military forces who have clashed since their youth. Their personal and professional conflicts escalate when both are vying for Raeliana's affection.

Justin's key relationships drive much of his involvement in the plot. His bond with his sister, Vivian, is strong but is tested by their differing roles and her schemes as an antagonist. His dynamic with Noah is a mix of professional rivalry and personal animosity, though it is noted that they are amicable rivals in swordsmanship. His relationship with Raeliana begins as admiration but grows into a sincere romantic pursuit, leading to direct conflict with Noah during key events, such as the Foundation Day Festival, where the two men openly compete for her attention. His commander, Siathrich, also serves as a mentor figure to whom Justin is loyally devoted.

Justin is noted for his remarkable abilities, primarily his exceptional skill with a sword. His prowess is such that he is considered one of the best swordsmen in the kingdom, with his abilities rivaling and matching those of Noah Wynknight. This skill, combined with his training and discipline, makes him a formidable knight and a point of pride for his family. Throughout the story, he develops from a capable but perhaps overlooked young knight into a growing leader who inspires those under his command, demonstrating conviction and reliability on the battlefield. His honest and straightforward nature makes him a compelling figure who stands as both a loyal protector and a serious contender for Raeliana's heart.