Garfiel has short gold hair and jade colored eyes. He is slightly taller than Ram, has a scar on his forehead, and has feline like canines.
Unlike his older sister Frederica, Garfiel uses his mother's surname Tinsel to remember her. He was initially hostile to Subaru, as he wanted to protect the people in the Sanctuary since he believed the outside world to be a terrible place. However, with Subaru and Ram's help, he was able to face his past and overcome it. After making up with Subaru, he begins to call him boss. He has feelings for Ram and uses various proverbs to try and impress her to no avail. As a 14 year old, he also exhibits some chuunibyou tendencies, frequently being impressed by Subaru's naming sense.
Garfiel was born around 14 years ago to a father who was a half and a Human mother, Reala Thompson, and was born a quarter. Eventually, after wandering around, Frederica, along with Reala and Garfiel, were picked up by Roswaal and given a home at the Sanctuary. Reala left her children at the Sanctuary to bring back her missing husband.
Garfiel and Frederica lived together until she left when he was 4 years old and he hadn't seen her since until their reunion 10 years later during the Sanctuary incident. After seeing his mother's "death" during the trial at a young age, he began to fear the outside world, causing him to try and protect the Sanctuary, however he was convinced otherwise once Subaru and Ram successfully talked him into facing his past in the trial.
Divine Protection (加護 Kago): Garfiel has the Divine Protection of Earth Spirits (地霊の加護 Chirei no Kago). As long as he has his feet on the ground, his body is covered in a tough guard of earth. He can cause the earth to cave in with a single step, reduce the effects of Earth Magic, and accelerate the recovery of wounds and stamina.
Beastification: Calling back on his ancestral Demi-Human blood, Garfiel can fully or partially transform himself into a huge golden tiger, however if he completely transforms he loses his reason, making him avoid it if possible.
Magic User: Garfiel has some decent skill in Water Magic.
- Healing Magic: Garfiel summons water mana to heal the wounds of himself and others, however it only affects physical ones. Power varies by the skill and talent of the individual or partially that of the spirit if the caster is using Spirit Arts.
Flowing Battle: Garfiel's wild combat-style which relies on instinct and his superior physique rather than finesse to perform maneuvers only he can do.
Equipment: Garfiel uses two shields in combat.
- Pyroxene Crystal (輝石結晶): When Garfiel was younger, he and his sister Frederica both received a Pyroxene Crystal from their mother Reshia Tinsel.
- According to the author, Garfiel's birthday is October 12.
- According to the author, Garfiel is scheduled to be featured in Arc 7.
- He originally learned Healing Magic as one of the ways to support the residents of the Sanctuary.
- It was revealed that the secret behind Garfiel's strength is an old book about Reid Astrea. In that book, an unknown person described Reid's training in detail. Garfiel took the training regime to heart and spent his entire childhood training like Reid. Interestingly enough, the training primarily consists of hand-to-hand combat, without any weapons whatsoever.