In-Depth
Yamato grew up without a father and was raised by his single mother. As a kid he learned how to take care of himself and their house when his mother was away from home— making meals and cleaning the house. After his mother passed away, his grandmother from his mother's side took him in. Thus furthering his abilities to cook and clean.He loves space, stars, and constellations. Yamato had aspirations to be an astronaut when he was a kid. However he dropped this dream when he got a cavity, thinking "I’ll never become one now." This lead him to get into physics and eventually become a physics teacher.
Due to his upbringing, he is a homebody and continues to love cooking into his adult years, often making breakfast and dinner. His apartment is very minimalistic and he has a Roomba, whom he considers his pet. He is scared of dogs due to being attack by one as a kid.
Yamato is popular and well liked. This is evident in the games and within the fandom. On the surface, he is conceited and doesn't deny his popularity, especially with women. Honest, blunt, and straightforward but beyond the surface, he is thoughtful, caring, nurturing, and compassionate. So while he doesn't hide his popularity with women, he honestly is not vain.
Yamato enjoys the cute, angry faces MC makes and the two are often bickering and bantering about silly things together. She usually pouts during these interactions which leads to Yamato giving MC the infamous nickname, Pouty. Additionally, he'll pinch and poke her cheeks, commenting on the softness and compares them to his favorite food, warabi mochi.
When it comes to romantic things, he blushes and shies away a lot. Yamato is label as a tsundere and/or an ore-sama and while he does have traits of both tropes, he is written in a much softer tone. Sometimes character tropes are written too extreme into the character so it feels force. In my personal opinion, Yamato is written with the perfect balance, which is why I feel so drawn to his character.
At the all-girls high school he teaches, both his work colleagues and students highly respect him. Except the Vice-Principal. More on that in Story... He is a stern teacher and makes sure his students focus in class and on their studies. Most of his students have crushes on him but he dismisses them merely as just crushes and nothing more.
With his friends, Yamato is more lax. Often joking around and throwing a few insults at eachother, but there is warmth to it and they mean well.