Garfiel Tinsel is a character who appears as a transfer student in the third season of the anime Isekai Quartet, originating from the series Re Zero Starting Life in Another World. He is the younger half brother of Frederica Baumann, and he chooses to use his mother's surname, Tinsel, as a way to honor and remember her. Garfiel is a young man, approximately fourteen to fifteen years old, recognizable by his short golden hair, jade colored eyes, and distinctive feline like canine teeth. A notable scar on his forehead serves as a physical reminder of a traumatic incident from his childhood.

Garfiel’s personality is a blend of aggressive impulsiveness and a deep seated loyalty. Initially, he comes across as wild and confrontational, driven by a powerful desire to protect the people of the Sanctuary, a place he considers his home. This defensiveness stems from a childhood trauma where he witnessed his mother's apparent death, leading him to believe the outside world is a terrible and dangerous place. Despite his rough exterior, he is honest, holds a strong sense of honor, and secretly enjoys reading heroic tales, showing a more thoughtful side. He is also in the midst of an adolescent phase, exhibiting chuunibyou like tendencies where he is easily impressed by dramatic names and ideas, to the point of adopting the alias Gorgeous Tiger. A distinct verbal trait is his habit of frequently using proverbs, many of which he makes up on the spot, often failing to use them correctly in his attempts to sound wise or impress others.

Garfiel's primary motivation throughout his story is overcoming past trauma and fear. His actions are initially driven by a fear of loss, causing him to oppose anyone trying to open the Sanctuary to the outside world. He is personally motivated by a long held, albeit often unrequited, romantic affection for Ram, and he constantly tries to gain her favor. In the context of Isekai Quartet, he and Otto Suwen join as new transfer students, bringing their dynamic into the comedic setting of the school.

His key relationships are central to his development. His initial hostility towards Natsuki Subaru transforms into a deep respect after Subaru helps him confront his past, leading Garfiel to affectionately call him boss or commander. He shares a brotherly bond with Otto Suwen, whom he sometimes calls Brother Otto, and the two often find themselves in comedic situations together. His feelings for Ram are a major part of his character, and despite her cold demeanor and consistent rejections, she does play a role in helping him face his inner demons. Another significant relationship is with Mimi Pearlbaton, who develops a strong infatuation with him. While he finds her annoying at first, Garfiel gradually learns to care for her and feels immense guilt when he fails to protect her.

Garfiel is a formidable fighter, considered one of the strongest members of the Emilia Camp. His primary ability is the Divine Protection of Earth Spirits, which grants him enhanced defense, accelerated healing, and the power to manipulate the earth beneath his feet as long as he is in contact with the ground. His most iconic power is beastification, a transformation that taps into his distant demihuman lineage, allowing him to turn partially or fully into a massive, powerful golden tiger. While this form drastically increases his physical strength and regenerative capabilities, he risks losing his rational mind if he transforms completely. In combat, he wields two shields and uses a wild, instinct based fighting style that relies on his superior physique and reflexes rather than formal technique. He has also learned water magic specifically for healing, which he developed to support the residents of the Sanctuary. His power is such that he has fought deadly opponents like Elsa Granhiert and the warrior Kurgan, and he acknowledges a significant gap in strength between himself and the Sword Saint, Reinhard van Astrea.