Sei is a Japanese office worker in her twenties who got pulled into the kingdom of Salutania through a Saint Summoning Ritual, along with another girl named Aira Misono. Her main power is a fifty percent effectiveness boost on anything she creates using magic—basically everything she makes hits twice as hard as it should.
The thing is, she wasn't recognized as the Saint right after the summoning. Her appearance didn't match what people expected, so they overlooked her. Petty? Maybe. But Sei was offended enough that she just. didn't tell anyone who she actually was. She only confirmed it later by checking her own status board. During her time at the Medicinal Flora Research Institute, people kept almost discovering the truth through her research work, but she managed to keep it under wraps until enough people witnessed her abilities firsthand and word got around.
Outside of work, Sei's into cooking and making cosmetics—she's basically turned that hobby into a real business in the capital. She's best known for her crafting abilities and the mysterious high quality of everything she produces, at least until the Saint thing came out publicly.
Content compiled by AnimeList.moe from publicly available sources.