Aren't they breaking rule 5 though with the 2nd waifu has a partner
Cheating while having a partner vs. cheating while being married is a big difference in Japan.
Unlike many Western countries where infidelity merely influences asset division, Japanese civil law treats adultery (
fukin-koui) as a
tort (civil wrong) that directly damages the marriage. This gives the wronged spouse the right to seek direct financial restitution. They can sue both their cheating spouse as well as the person they cheated with.
This is why they have the rule about getting written consent if he’s sleeping with a married woman. It’s to eliminate potential financial liability.