Reiko Nishihori is the synchronization partner of Roidmude 050 and a minor antagonist in Kamen Rider Drive.
The daughter of Koya Nishihori, an infamous criminal known as the "Copycat Pirate", after her father was captured by Shinnosuke Tomari aka Kamen Rider Drive, Reiko began seeking revenge against the Kamen Riders. She later synchronized with Roidmude 050 to become Seeker Roidmude.
As the Seeker Roidmude, Reiko used her powers to make the whole population of residential areas go mad, allowing the Roidmudes to use them as synchronization partners. She also adopted the alias of "Yoriko Soma" to get close to Go Shijima / Kamen Rider Mach. Desiring to make a Kamen Rider commit murder, Seeker used her powers to drive Go mad so she could get Go to kill her. However, Drive stops Mach by knocking him out of his transformation. Seeker furiously attacks Drive, but Drive fends her off and overpowers her with Type Formula, before separating Reiko from the Seeker Roidmude with Type Formula Mantarn's Resurrection Fuel-backed punches, resulting in Seeker reverting back to 050. Drive then finishes off 050 with Trailer Impact.
Defeated, Reiko reveals her true plans to make Go murder her in cold blood to get a Kamen Rider to commit the worst crime imaginable before breaking down and crying as she was arrested by Shinnosuke.
Kamen Rider Drive Saga: Kamen Rider Mach
Two years after the second Global Freeze, Reiko was released from prison with advocacy from Go, but ends up being used by the Revenger Roidmude to get revenge on Mach. After the defeat of Revenger, Reiko becomes a couple with Go.