Hien is a supporting character in Log Horizon, known for being a high-ranking member of the Crescent Moon Alliance guild where he serves as one of its Team Leaders. His in-game avatar is of the Fox Tail race and he takes on the Assassin class, specifically the Assassin-Rogue archetype. Despite the wide selection of weapons available for his class, Hien prefers to use a crossbow, allowing him to operate effectively as a sniper from a distance rather than engaging in melee combat. He is one of the few members of his guild who has reached level ninety, demonstrating a high degree of competence in the game's mechanics.

Before the Catastrophe that transported the players into the game world, Hien was a first-year high school student in the real world with the given name Madoka. He is not particularly fond of his real name, though his discomfort with it is not as pronounced as that of his guildmate Henrietta. He is classmates with several other members of the Crescent Moon Alliance.

Hien is characterized by a mischievous and playful personality. This trickster nature frequently gets him scolded by his companions, but it is a core part of his interactions with those around him. His most notable relationship is with fellow Crescent Moon Alliance member Shouryuu. The two share a friendly and competitive rivalry and are almost always seen together. Their dynamic often involves bickering and laughing, and their contrasting personalities, reminiscent of a fox and a wolf, make them a distinctive pair within the guild.

In the early days following the Catastrophe, Hien assisted in Shiroe's plans to revitalize the city of Akihabara. His contribution largely involved helping Shouryuu hunt and capture boars, which were then provided to chefs to be butchered for maximum meat yield. Though he plays a minor role in many of the main story arcs, his involvement deepens when he participates in the Shibuya Raid Team alongside guild leader Maryelle, Henrietta, and Shouryuu.

Hien has a significant connection to a Landers girl named Nanami. He befriended her after retrieving her favorite jar, which had fallen through the floor of her room and into the city sewers. This act of kindness forged a bond between them, and Nanami later joins the Crescent Moon Alliance as a junior member, often seen looking for Hien. This relationship originates from the side story Honey Moon Logs, a narrative from which Hien, like several other characters, was adapted into the main light novel and anime series.