Anyone notice how Aya gives Marika 10k per day instead of 1m at the end, even though Marika has to give the money back if she fails either the wager or the contract? That's a manipulation tactic. If she were to give Mari the money at the end, Mari could quit at any point and not feel any loss. Whereas by giving the money to her a little at a time, the situation changes from "I could lose out on the chance for 1m" to "I'll be losing 500k." It's taking advantage of loss aversion and the sunk cost fallacy to keep Marika hooked. Highly suspicious.
Just gonna put this out there but Aya doesn't give the money to Marika every day. That conversation about "10k per day" was her averaging the whole thing out in perspective.
The terms of their bet was Aya giving ¥1M to Marika if Marika wins at the end of those 100 days and does not fall in love or acknowledge that same sex relationships can work (much less apply to her). Aya wins and will get to keep the money if she manages to convince Marika that it's a possible route.
The only time any sort of "transaction" ever happening between them was when Aya gave Marika a bag worth ¥30k as "down payment".
Not saying it's better but from a different perspective, it wouldn't be too far fetched to put it at a similar situation as giving your significant other/person you're courting a slightly expensive gift. IF the bet was never the in place.