He formerly played soccer with Enta, where they were known as the "golden duo", though he quit the sport immediately before the events of the series. He also dresses as the idol Sara Azuma to take selfies for his brother Haruka.
Kazuki is a middle school student with reddish-brown eyes, burgundy spiky hair. He usually wears a white shirt with light blue markings on the collar and short sleeves, a red tie, long blue trousers, and black shoes.
In later episodes, he is seen in a different casual outfit that matches the rest of his family, consisting of a long-sleeved, white shirt with pink stripes and a pink shirt over it. The pink shirt seems to have a cartoon image in the middle of a kappa sitting in a fetal position with the characters under it reading 'Ka-e-ru' which roughly translates to 'I will change'.
In the manga, he has the same appearance, only with a different art style (by MiGi) and most of the time in black and white.
In his Kappa form, he retains the same hair color and a similar style but features a sara (plate)  on his head, with a large red neckerchief around his neck.
His skin color in his kappa form is a light green hue with a lighter chest and stomach area with large black eyes. His arms and legs are small and thin with three smaller digits as fingers and toes. The shell on his back has a swirly pattern on it.
He demonstrates exceptional confidence both when playing football and thinking nothing of dressing as Sara Azuma and photographing himself in a selfie with Toi as he was breaking into a car. It is his suggestion to kidnap the real Sara Azuma and take her place in a fan meet and greet event, planning and taking part in the scenario. Kazuki cares a lot for his younger brother, messaging him each day in his Sara guise to give him the impression of a personal relationship with the star.
He is further supportive of his childhood friend Enta, upon finding out that he had kissed him in his sleep and had feelings for him, Kazuki passed it off as Enta doing it having been dared to mitigate any possible embarrassment. Additionally, when Enta's life was in peril, he did everything in his power to try and save him. The same was applied for Toi.
Main article: Kazuki Yasaka/Story
- His personality is earnest (in his opinion) 
- His most favorite food is Kappa maki, while his least favorite food is Omurice 
- His recent obsession is soccer. 
- His height, blood type, and motto are the same as Sara Azuma's. 
- For now, I want to build real connections with the people that are within my reach. - Kazuki's monolog (ep. 7)
- Episode 1
- Episode 2
- Episode 3
- Episode 4
- Episode 5
- Episode 6
- Episode 7
- Episode 8
- Episode 9
- Episode 10
- Episode 11
Kazuki appears in all eleven episodes of the Sarazanmai anime.
- Pash! Magazine
|Anime||Episode 1 ア Episode 2 ア Episode 3 ア Episode 4 ア Episode 5 ア Episode 6 ア Episode 7 ア Episode 8 ア Episode 9 ア Episode 10|
|Characters||Arcade Attendant ア Chikai Kuji ア Enta Jinnai ア Gang Leader ア Hanayashiki Amusement Park ア Kazuki Yasaka ア Kazuki’s Grandpa ア Kazuki's Mother ア Keppi ア Kiis Memore ア Mabu Akutsu ア Nyantaro ア Nee-chan ア Nekoyama Mokichi ア Otone Jinnana ア Police Officer (One) ア Police Officer (Two) ア Reo Niiboshi ア Sara Azuma ア Sara's Manager ア Soccer Player (One) ア Soccer Player (Two) ア Sword Gang Member ア Toi Kuji ア Usoo-kun the Otter ア Yurikamome Gangster ア Zombies|
|Manga||Main Series: Sarazanmai (Manga)|
|Reo and Mabu: Together They're Sarazanmai: Chapter 1 ア Chapter 2 ア Chapter 3 ア Chapter 4 ア Chapter 5 ア Chapter 6 ア Chapter 7 ア Chapter 8 ア Chapter 9 ア Chapter 10 ア Chapter 11|
|Media||DVD's: Volume 1 ア Volume 2 ア Volume 3 ア Volume 4 ア Volume 5 ア Volume 6|
|Music: Kawausoiya ア Massara - Kana Boon ア Sarazanmai no Uta ア Stand by Me - The Peggies|