Hobsei, also known as Sei, belongs to the goblin tribe’s generation preceding Rou’s arrival. She crucially influenced tribal leadership by proposing a duel between Rou and the reigning hobgoblin leader, Gobkin, preventing internal strife and cementing clear authority. This action enabled Rou’s rise to power and secured her place within his core leadership circle.

Initially a Hobgoblin Mage, Hobsei exhibits extraordinary devotion to magical study and combat. Her relentless pursuit of arcane mastery propels her evolution into a "Spell Lord," marking a profound leap in her species' capabilities and magical prowess. This transformation stems from accumulated experience and rigorous training, amplifying her command of elemental and arcane forces. Later, she advances to a "Half-Spell Lord" state, refining her specialization and power in resonance with Rou’s own evolution. Distinctive tattoos manifest during this process, symbolizing their connection.

Hobsei shares a steadfast romantic bond with Hobsato (Sato), another hobgoblin of her generation, a constant thread in her personal story. Within the tribe and later the mercenary unit Parabellum, she serves as Rou’s trusted subordinate, delivering strategic magical support in conflicts and missions. Her abilities rank her among Parabellum’s most formidable magic users.

In combat, she unleashes potent spellcasting, wielding elemental affinities honed through her Spell Lord evolution. This grants her versatile battlefield control and devastating offensive impact. Positioned among Rou’s upper-tier allies, her magic-based supremacy eclipses numerous other races and evolved beings in their sphere, including ogres and elite combatants.