If you remember dialogues from LSHRM, Seiya only marries her to use her as a test subject for Flower project. Even after that he lets his coworkers fuck her in exchange for favors. Reiko is one who he truly loves even though he sleeps with Yoshimi or Masao's friends sometimes.
I think you would have hated him even more if you played the LSHRM questline I've planned. You get back at him at the end of the quest in both endings.
Be prepared to hate these characters in Magic Ring:-
- Mr. Kobayashi
- Nagito
- Mr. Yamada
- Nobuko
- Kunio (not really if you like Kasumi)
- Asuka (might like her later)
Only the one you see in 305 is Ousam. Others are real Masuo interactions.