FIRST:
The game's winnings doesn't matter at all. They only decide rankings. Because game wise, no one was in debt and everyone only won.
NOW:
Think of it like "If I know I'm gonna win and all my debt gonna get reduced to the loser's, then why not I collect more debt?" After all, all will be transferred to the loser and I'll get his (Jun's), a much smaller amount than what I've borrowed.
THUS:
Mary borrows ¥260 million, her total now 50+260= negative 310 (+260 currently held by Suzuki).
CONCLUSION:
At the end Jun gets all ¥310 debt million to his side and his ¥10 million is still owed by Mary. But she also now has those ¥260 million to herself. Thus,
• Mary has + ¥250 million,
• Jun has negative ¥310 million,
• Yumeko has negative ¥310 million AND negative ¥20 million of that chick,
• The chick's in the clear since despite her win, her debt of ¥20 million was lower than Yumeko anyways. Imagine if just like Mary, this chick had taken a serious loan as well. Yumeko would've been completely screwed.
