Couples' Finances: Common Wallet vs. Split?

The first thing to decide when living together is "Money Rules".
Leaving it vague leads to burden and resentment.
Here are 3 management patterns.

Pattern A: Common Wallet (Allowance System)

Both put a fixed amount (e.g., 100k each) into a common account/wallet. All living costs come from there.

• Pros: Easy to see total costs. Easier to save surplus. Good practice for marriage.
• Cons: Hard to spend on personal hobbies. You might judge partner's wastefulness.

Pattern B: Item-Based Responsibility

"He pays rent, She pays food & utilities." Splitting by category.

• Pros: Easy management. Less interference in each other's wallet. Low stress.
• Cons: Unfair burden (food costs vary). Rent payer's burden is fixed.

Pattern C: Pay & Settle (App Management)

Whoever can pay pays. Record everything in an app. Settle the difference at month-end.

• Pros: Earn credit card points individually. Perfectly fair (down to 1 yen).
• Cons: Recording is a hassle (habit is key). Need to avoid seeming "stingy".