Finn Ames is one of the main characters in the Mashle series, a first-year student at Easton Magic Academy who serves as the roommate of the protagonist, Mash Burnedead. He is also the younger brother of Rayne Ames, a powerful Divine Visionary. In terms of appearance, Finn has an average build with notably skinny legs. He has black hair with a distinct yellow streak on the left side of his fringe, and he often has freckles visible on his face. His magic mark, a straight line, appears on his right cheek running from his eye down to his jaw. At school, he wears the standard Adler robe, while his casual clothes typically consist of a shirt, waistcoat, and trousers.

Finn has a timid and easily frightened personality, often serving as the "straight man" to react to the strange and absurd antics of the other characters around him. He is shy and longs for a peaceful, trouble-free student life, as reflected in his favorite words being "peace and order". Despite his cowardly demeanor, he is extremely loyal and deeply caring toward his friends. On multiple occasions, he has shown a willingness to go to great lengths and endure significant hardship for the people he is close to, proving that his inner strength surpasses his outward fears.

Motivated by a desire to support his friends and avoid being a burden, Finn often pushes himself past his perceived limits. He also harbors a deep-seated wish to stand on equal footing with his older brother, Rayne, and be someone Rayne can rely on rather than someone who needs constant protection. In the story, Finn's primary role is as Mash's first true friend and roommate. He often acts as an anchor to normality, explaining the basic rules and common knowledge of the magical world to Mash, who is entirely non-magical. He also frequently acts as the voice of reason or provides comedic commentary on the increasingly ridiculous situations the group finds themselves in.

Finn's key relationships heavily define his character. His bond with Mash Burnedead is central. Although initially overwhelmed by Mash's eccentricity, Finn becomes Mash's most loyal supporter after Mash saves him from bullying. Finn is willing to risk his life for Mash's future, and Mash, in turn, fiercely punishes anyone who harms Finn. His relationship with his brother, Rayne Ames, is more complex. Having grown up as orphans in poverty, Rayne became a Divine Visionary to create a better world for Finn. However, Rayne grew cold and distant from Finn out of fear that Finn would be targeted due to his position. Finn, feeling this distance is unnecessary, desperately wants to be close to his brother again, a rift that begins to heal when they fight together against a powerful enemy. He also forms a mentor-student relationship with Divine Visionary Kaldo Gehenna, who recognizes the hidden potential in Finn's unique magic.

Throughout the series, Finn undergoes significant development, transforming from a self-doubting boy who feels inferior to his brother and others into a more confident individual who finds courage through his friendships. A major turning point occurs when he awakens a second magic line during a desperate battle, greatly increasing his magical power. Finn's notable abilities revolve around his personal magic, Changeas, which allows him to instantly swap the positions of two designated targets. This ability is highly versatile, useful for evading attacks, countering enemies by making them hit each other, and potentially even healing injuries. After unlocking his Secondth, he gains a powerful technique called Butterfly Sanitatem, which summons a giant butterfly entity that generates magical butterflies to heal allies and share his magical power with them. Beyond his unique magic, Finn possesses a keen intellect and sharp observational skills, allowing him to analyze fast-moving strategies that others miss. He is also known to use a fake spell called Dangerousse as a distraction to allow him to flee from dangerous situations.