Mayuka is a synthetic being created by the demon Yuzuha, who combined a lock of Tenchi Masaki's hair with a strand of her own to produce a hybrid offspring. She appears as a teenage girl with short blue hair and amber eyes that turn red when Yuzuha controls her. Genetically, she is confirmed to be Tenchi's daughter, and the Masaki household initially speculates that she might be from the future. Her true origin lies in Yuzuha's centuries-old grudge against Tenchi's grandfather, Yosho, and her desire to use Mayuka as a tool for revenge.

Mayuka's personality is sweet, naive, and gentle when free from Yuzuha's influence. She quickly forms a close friendship with Sasami, who accepts her without suspicion, and longs to be part of the Masaki family. However, Yuzuha manipulates her from afar, overriding her will and compelling her to attempt the kidnapping of Tenchi. When Mayuka fails, Yuzuha erases her memories and takes direct control, transforming her into a mindless killing machine. Despite this, Mayuka's innate kindness resurfaces when Sasami pleads with her to spare Tenchi, proving that her true self remains intact beneath the demonic influence.

Her motivation throughout the story is conflicted: she genuinely seeks a father's love and a place to belong, yet she is also a pawn in Yuzuha's scheme. After breaking free of control, Mayuka attacks Yuzuha in defiance, leading to her death when Yuzuha shatters her into a red crystal. Following Yuzuha's defeat, Washu uses the crystal to resurrect Mayuka as an infant, giving her a second chance. The Masaki family agrees to raise her as their own. Notable abilities include superhuman strength, the power to summon a faux-Lighthawk sword that mimics Tenchi's signature weapon, and the capacity to fight fiercely when under Yuzuha's thrall. Her development arcs from a confused, manipulated newcomer to a courageous individual who chooses to rebel against her creator, and finally to a reborn child welcomed into the household.