The wife of Paul and the mother of Rudeus and Norn.

Zenith was born in the Holy Country of Milis, as the second daughter of an earl of Milis. She grew up following the Milis Church religion, never breaking the rules, getting good grade in school, and had nickname Milis young lady standard. But, when Zenith reached the age of 15, she rebelled against her parents and ran away from home.

While trying to find a job as a Healer, she was a solo adventurer for a time. However she was frequently conned out of a large amount of money due to the little knowledge she had on how expensive healer's are, but was saved by Paul Greyrat. She then join Paul's party, the Fangs of the Black Wolf, as a healer. She spent a long time in the party as a healer and gradually began to fall in love with Paul and wanted to marry him. However Paul was a womanizer who frequently slept with multiple women and she didn't want to be with someone like that so she told him if he promised to be faithful to her then she would sleep with him, to which he agreed.

Shortly after, she became pregnant with Rudeus and as a result both her and Paul retired from adventuring and settled down in the countryside.
Due to the Metastasis Event, she was transported inside a magic crystal in a hydra's lair in a dungeon. When saved, however, she lost all her memories and reverted a vegetative state due to the effects of the crystal. Lilia now cares for her incapacitated self.
It was later revealed that though Zenith seems to be in a vegetative state, she is actually aware of her surroundings.
(Source: Mushoku Tensei Wikia)