Seiko Oomori (大森靖子; born September 18, 1987) is a Japanese singer-songwriter and performer from Matsuyama, Ehime. She studied at Musashino Art University, then began her career in Tokyo's Kōenji underground scene. After a brief period in the punk band Kuchuu Moranko, she went solo. Active since 2011, she also led the four-piece band 大森靖子&THEピンクトカレフ before making her major-label debut with Avex Group in 2014. Her work spans alternative pop, alternative dance, and J-pop, and draws on idol culture and punk rock.
Alongside her solo releases, Oomori has also worked in collaboration and production. She provided "Fuku o Kite, Koishitai" to Iginari Tohoku San, performed "JUSTadICE" for Black Clover, and performed "Sacchan no Sexy Curry (さっちゃんのセクシーカレー)" for Shokugeki no Souma.
In 2018 she formed the idol group ZOC and joined it as a member. She later restarted ZOCX and produced the idol unit Zettai Shoujo. After undergoing surgery to remove vocal cord nodules in 2023, she marked the 10th anniversary of her major debut in 2024, then ended her Avex Group contract and announced a 47-prefecture tour in 2025.
