Tsukiko Masaki grew up in Masaki Village as part of the youngest generation descended from Yosho and Kasumi. Her position within the family hierarchy was reflected during events like the pre-party for Rea's wedding, where her later arrival placed her at the farthest end. She studied artificial intelligence at Galaxy Academy, meeting and marrying Ken Raraiba Steinbeck there, while also receiving affection from researcher Hiroshi Manada. After Ken's mysterious death in space, Tsukiko entered a relationship with Dai Tennan, resulting in the birth of her son Kai Masaki. This relationship deteriorated due to Dai's childish and feckless behavior, leading Tsukiko to restrict his access to Kai. She already had a daughter, Kiriko Masaki, from her marriage to Ken. Tsukiko frequently brought Kai to visit his distant cousin Tenchi Masaki, as they were close in age. Kai befriended Seina Yamada at school, who also became friends with Tenchi. This connection led Tsukiko to meet Seina's mother, who thanked her for Kai being Seina's first friend despite Seina's extreme bad luck. Young Kiriko witnessed this interaction, beginning her close bond with Seina. Tsukiko adhered to Masaki Village tradition by not revealing their alien heritage to Kai until he came of age. Kiyone Masaki, Tenchi's mother, acted as a second mother to Kiriko and Kai and passed away in Tsukiko's home while watching over them. As Seina grew older, Tsukiko developed romantic feelings for him. She scolded Kai after discovering him and Seina with inappropriate magazines and appeared willing to offer herself to Seina before an interruption. Her cousins Fuka, Otoka, and Mizune Masaki later encouraged her to pursue Seina. During Seina's first trip to Jurai, the shapeshifter Kuis Panta impersonated Tsukiko, kissed Seina, and declared love, claiming to express Tsukiko's genuine feelings. This prompted an embarrassed confession from Tsukiko, where she explained plans to marry Seina if he stayed on Earth, though she later clarified to Kiriko she hadn't abandoned this possibility entirely. Tsukiko played a significant role during events surrounding the 2023 OVA series *Tenchi Muyo! GXP Paradise Starting*, coinciding with Seina's return from Renza. After Kai became engaged to Seina's sister Yoshiko Yamada and moved into the Yamada household, Seina's possessions were relocated to Tsukiko's home. When Seina spent a night there, Tsukiko confessed the marriage plan devised by her and Masaki Village, revealing Kiyone Masaki as an early advocate. She reiterated her willingness to marry him and emphasized her feelings through close proximity. During this period, Tsukiko bonded with most girls accompanying Seina—Fuku, Miki (who called her "mother"), Kirche, D, and Nayuta—but maintained an intensely cold relationship with Jovia Jovis, often reacting violently to Jovia's statements. The other girls expressed openness to Tsukiko joining as a future bride. After the relocation of Tabletop Island, Seina facilitated Tsukiko's introduction to magic within the Kamidake's subspace. She demonstrated rapid mastery of complex magic and exhibited memories of ancient magic users unknown to others, suggesting potential to surpass Seina and Jovia in magical ability. Her absence from the fifth season of *Tenchi Muyo! Ryo-Ohki*, despite her children and Miki appearing nearby, remained unexplained but was expected to be addressed in future GXP OVA installments. Tsukiko harbored discomfort regarding Kai's resemblance to his father Dai, admitting she loved Kai as a son but disliked him as a person due to these similarities. Despite relatives suggesting she let Dai assume responsibility, she remained determined to oversee Kai's upbringing herself. Her lifelong passion for fantasy novels about magic and creatures influenced both her daughter Kiriko and Kiyone Masaki, potentially shaping Kiyone's research into reaching the parallel world Geminar.