Forward yen appreciation, dollar depreciation, long-term depreciation of currencies with high interest rates in line with interest rate parity, dollar depreciation rate (swap rate):

(124-123.8) * 2/124 = 0.323%, which is lower than the spread.

Arbitrage steps: borrow yen, immediately convert it into dollars, invest for 6 months, and sign a forward contract to sell the principal and interest of dollars for 6 months. After 6 months, the investment principal and interest of the US dollar will be recovered, sold at the forward contract price, converted into Japanese yen, and the loan principal and interest of the Japanese yen will be deducted, which is the profit. The arbitrage profit per unit yen is:

1124 * (1+5%/2) *123.8-(1+3%/2) = 0.008347 yen.