"It's Momo Sagara☆Nice to meet you-nyan"
- —Momoka, Valkyrie Drive Mermaid
Momoka Sagara is a mysterious girl who was transferred to the "Mermaid" island later on, other than Mamori and Mirei. She awakened as an Extar already during the bird's arrival and her abilities are quite high. She is cruel to the pure ones due to her wild personality, who is not scared of anything. She often bears a discord with others by their behaviour and disturbs her surroundings.
Momoka has light-blueish hair that is tied in a bow with two long pieces of hair flowing out reaching almost to the ground. She has a cat hair clip similar to Mamori's clipped at her bangs. She has turquoise eyes.
She wears a black bluish jacket with a yellow bow wrapped around her collar. To accompany it she wears a short skirt black-blue boots, a black glove on her right hand and a stocking on her left leg.
Momoka is very manipulative and sadistic. She was able to easily manipulate Charlotte into going along with her plan to expose Akira's true gender. She is also quite insightful as she was able to see through Akira's disguise instantly upon meeting her. She is also quite sociopathic. However, she always drives herself into malicious insanity when fighting her enemies, due to her maniacal behavior.
- She was Mirei's previous Extar.
- As seen in episode 9 she can enter drive with anyone.
- She is a third generation Soldier Arm Extar.
- She belongs to an unknown organization sent to the Island Mermaid for a mission to retrieve the girl (Mamori) who generated the Valkyrie Effect seen in Episode 8.
- In the last two episodes (11 & 12), she was revealed that she was using Drive to Mamori and her teammates. Meaning that her true identity of Momoka was a "Hybrid" along with Lady J & Rain Hasumi.
- Momoka's code name is A3.
- Her motifs are Gentoku Himuro (A.K.A, Kamen Rider Rogue) and Nariaki Utsumi (A.K.A, Kamen Rider MadRogue) (in case, both them as Night Rogue) from Kamen Rider Build. In strange fact, both Momoka, Gentoku, and Utsumi have malicious nature and insanity themselves.