Tatsuya Sawamura is a minor character.
He's the son of Shinjirō and Yoshiko Sawamura, brother of Junya, grandson of Yoshito Sawamura, nephew of Giichirō Sawamura, Seisaburō Sawamura, and Rumi Satō, cousin of Yūta, and Anju.
Two years prior, Tatsuya and his brother Junya got scared when their grandpa Yoshito's broke in to rescue their cousin Anju from their home.
Tatsuya and his family attend the grandpa Yoshito's funeral, and Tatsuya and his brother Junya just play games. They mock their cousin Anju. After Anju escaped, they later see her in a car with their uncle Seisaburō, and run to tell their father.