Seiko comes from class three is one of the new mikos who make up the Miko Council. She's a very out going person. In fact one could swear she was the leader of the group rather than Yuzu. She has a gift for taking charge. She also doesn't have much luck in relationship. Chika is her best friend or at least that's what the anime implies. Her main weapon is a type of Spear. Seiko is one of my two favorite Mikos. The other being Chika. Depending how I feel, I sometimes like one slightly more than the other.
Attacks

Lady-Tremendous One Slash! The Maiden Deplorable Blow Slash! Maiden's Full Power Spear Strike! Maiden's Tremendous Spear-Strike! all are used for the same exact attack. This consists of Seiko spinning the spear around and then jump in the air to dive and strike at an enemy. Now as for why an attack needs so many names just watch the show itself.

Maiden's Regret Spear-Strike!: Seiko throws the Spear itself toward an enemy. Ie straight up at them.

Lady Full Bloom One Slash!: Seiko spins the spear and throws it. When she does the spears spins like as it has become a wheel on it's side flying through the air.