Summary
If you make 2,128,884 円 a year living in Japan, you will be taxed 400,351 円. That means that your net pay will be 1,728,533 円 per year, or 144,044 円 per month. Your average tax rate is 18.8% and your marginal tax rate is 20.9%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 円 in your salary will be taxed 20.85 円, hence, your net pay will only increase by 79.15 円.
Bonus Example
A 1,000 円 bonus will generate an extra 792 円 of net incomes. A 5,000 円 bonus will generate an extra 3,958 円 of net incomes.