Uno (ウノ Unou) is the pet of Mashiro together with Seno, who combines with her to get Mashiro in her Taller Form. Uno and Seno are called sheeps by their owner, though they look like Chicks. Uno is one of the main protagonist of the series, Kamikami Kaeshi.
From the name Uno, means One or First and Seno, which means Of The Back. This overall means that Uno is the first and Seno is a last.