Yui belongs to the Maple Tree guild in the VRMMORPG New World Online. She is one of the twin sisters, paired with Mai, recruited into the guild by Maple and Sally. The game's first two floors feature distinct yet harmonious environmental themes reflecting Yui and Mai's relationship.

Yui employs an extreme strength-based build, dedicating all stat points to physical power (STR) and wielding massive hammers. This contrasts directly with her sister Mai's focus on intelligence-based magic attacks. Together, they fight in unison, forming a balanced combat duo that overwhelms opponents. A key development occurs when Maple aids the twins in securing powerful new skills. This results in Yui acquiring the unique ability [Conqueror], which alters the standard stat point distribution ratio. Similar to Maple's [Absolute Defense], [Conqueror] significantly enhances Yui's strength-focused build, enabling her attacks to inflict exceptional damage.

Yui's progression demonstrates unconventional character development. Her singularly focused build appears initially impractical but becomes highly effective through strategic skill acquisition and synergy with Mai. Their coordinated combat style and complementary roles make the twins integral to the Maple Tree guild's success in events and boss battles.