Since rigald00 has only summarized (very poorly) about the characters, let's expand for anyone new coming in:
The dad: He's a single father who still misses his wife and is strict about his son's upbringing, but clumsy about his own life. They have a healthy relationship and he occasionally has to be the voice of reason between the MC and heroine.
The fiance: She's a shut-in with a crippling social phobia (as if it's the scariest thing ever), is very shy, and spends money because she's allowed to. Since then she's learned to slowly overcome her weakness, wanting to be a good fiancee for the MC and repay the dad's kindness and has even gone out to get a job.
The MC: Unlike most MCs, he's still in middle-school, meaning he's about 14. Because he's very rigid in his goals and short-sighted due to his youth, he acts out and is quick to reprimand others while blind to his own shortcomings. At first he wanted to get rid of the fiancee, but now he's trying to reform her to become a person of society. He's still very much against the arranged marriage. He's his own main antagonist, so it'll be fun to see him grow up and calm down.