Satou Matsuzaka is a main character in the psychological horror series Happy Sugar Life. A freshman at Makikou High School and primarily works at Cure á Cute, maintaining a kind nature and getting along well with other people in order to sustain her lifestyle with Shio. Satō (さとう) means "Sugar" in Japanese. Her birthday is on December 31st. The biggest horror element of the series being the fact that Satou is in love with a minor whom she keeps captive in her apartment - and that it's to the point of deranged behavior and obsession.
- She befriends a mysterious young girl named Shio Kōbe, and immediately falls in love with her. She learns to love for the first time after meeting Shio and lives with her in a shared apartment. Publically, she tells people that she resides with her aunt in her apartment, and keeps the fact that she lives with Shio a secret.
- She vows to protect that feeling of love she bears for Shio, even if it means committing murder.
- Her wish is to spend her time with Shio forever in their apartment, she is aware of the fact that they cannot live on peacefully if she does not work and earn money for food, utilities, etc. Because of this, Satou often has to confront the outside world where people interfere with her relationship due to her past history of accepting anyone who has confessed to her and changing partners every three days.
- Satou is prone to severe animosity when people disrupt her relationship with their interpretation of "love", and can be easily provoked when it comes to Shio due to her overprotectiveness. She is willing to take any action necessary to eliminate threats to Shio and their Happy Sugar Life.
- After meeting Shio, Satou still acts kind around others in order to sustain their lifestyle, however, she no longer pursues relationships or allows people to pursue her due to her devotion to Shio and how she made her feel "complete". Because this, Satou develops a reliance on Shio to fill her life with happiness and "sweetness".
- Shio's reliance causes her to be extremely obsessive and protective of her and their relationship. Without Shio, Satou becomes immensely sad, empty, and heartbroken, doing whatever it takes to restore their relationship and even going so far as to kill anyone who threatens her "Happy Sugar Life".
- Ideally, Satou wishes to build a castle for her and Shio to live in and spend their days together forever, away from the corrupted and filthy outside world.
- Murder is always Satou's last option when she has to deal with people who may ruin her life with Shio. After all, now she knows how hard it is to safely get rid of bodies and clean bloodstains. It's much more efficient to bribe and manipulate them into doing what she wants. Many of her behavioral symptoms are tied to the Yandere trope.
- Satou's love for Shio is interesting. Satou is like a mother, sibling, and romantic lover (all at once) to Shio. This can be seen in their relationship, which is innocent with no lust or "bitterness" and the way Satou protects and cares for Shio.