In Japanese, there exists a special set of kanji called daiji (大字) for the numbers. The daiji (大字) are used for important financial statements. In the past, the kanji for the numbers we normally use could be easily manipulated to change for the benefit of the person. For example, all you need to do is to add another stroke and the kanji for one and change to two.
Some of the daiji (大字) have retained the same exact kanji for the numerals we use for numbers. I’ll provide a list so that you can compare the daiji (大字) and the kanji we use today for numbers. To make matters complicated, there is also a separate set of daiji (大字) that you can still see when you read very old Japanese literature. The numbers from this set are obsolete, but I’ll add them just for fun.
1 : more commonly used kanji for 1(一). The daiji in use today: (壱). The obsolete daiji: (壹)
2 : common kanji (二). Current daiji (弐). Obsolete daiji (貳).
3 : common kanji (三). Current daiji (参). Obsolete daiji (參).
The current daiji and the kanji from 4-9 are the same. The obsolete daiji are not the same, but I won’t bore you with the details, since you probably won’t ever see the obsolete daiji.
10 : common kanji (十). Current daiji (拾). Obsolete daiji (拾).
On some financial documents, where people worry about the numbers being potentially manipulated, numbers like 210 are written as 弐百壱拾 instead of 二百十. The number 210 in daiji is written so that you could read it as: 2 (弐) is in the hundreds (百) place and 1 (壱) in the tens (拾) place. It’s written this way so that people won’t be able to change the numbers so easily. For example, with 210, you could easily add another stroke under the kanji for two so that instead of 二百十, you get 三百十. When you’re dealing with money and other financial records, you want to be as accurate as possible and prevent any sort of potential misuse of the numbers. Hence, the daiji was created.