Gareth highly reveres Lancelot. She seems to normally have a sunny, friendly disposition, and as a result she does not deal well with the stress of the slaughter performed under the Lion King during the Camelot singularity of Fate Grand Order, only wishing to be punished. She had "mummy-like bags" under her eyes after helping to defeat the knights who opposed the Lion King, and although she has "lily-white fingers that are more beautiful than anyone's", they become unrecognizably blackened from constant washing after combat.
During the "Camelot" Singularity, the Lion King, an alternate version of Artoria, summons Gareth along with all of the other knights with the exceptions of Bedivere and Galahad. She claims to require their service in order to perform the "Holy Selection" that will help counteract Solomon's destruction of the world. She gives the knights a half-day to ponder over serving her or going against her, Gareth fully believing that Lancelot will choose to serve the Lion King. She decides to serve along with Lancelot, Gawain, Mordred, Tristan, and Agravain, and they are inevitably forced to fight their remaining comrades who disagree with the Lion King and wish to slay her.
The knights serving under the Lion King emerge victorious, becoming the "Knights of the Lion King." The Lion King grants the knights "Gifts", Gareth's coming from a wish "avoid being defiled any further." Together, they march forward to fight the "False Crusaders" led by someone claiming to be Richard the Lionheart, although he is quite different than the real thing. Upon defeating the crusaders, only the "demonically strong" Servant calling himself "Richard" remains. Gawain believes that there is no way to defeat him without sacrifice. Gareth, whose heart had been shattered throughout their battles, killing her comrades, false knights, and the people of the Holy Land, charges forward, restraining "Richard" at the cost of skewering her own chest. Apologizing that she cannot bear with following that path they chose, she calls herself a fool and wishes to be punished. As the other knights hesitate, Agravain prepares himself, but Gawain ultimately slays "Richard" along with his sister.
Along with the other knights, Gareth is considered to be a top-class Servant.
Along with the other "Knights of the Lion King", Gareth received a "Gift" to aid her. Being granted Impurity, she wished to "avoid being defiled any further" after having slaughtered her comrades. The specifics of the Gift are unknown.
- ↑ Fate/Grand Order - Camelot: The Sacred Round Table Realm, Chapter 17
- ↑ 2.0 2.1 2.2 2.3 Camelot/Zero