Some days ago I had given you a fitting formula: 西＝に＋四 which reads nishi = ni+shi.
In Japanese this means: direction-west = (towards) + 4. It does not have much direct meaning. Indirectly 4 was created by cutting the kanji for nishi = west where the one part with 4 sides was to be remembered as 4 called shi . So phonetically also shi comes from nishi and diagramatically you see that the remaining ni is reperesented by the same “other part” after rotating it 90degrees >> (like this) >> に.
Just now thinking about it more I wanted to compare all other digits and found that they are indeed present in this single kanji. In other words all digits were created from this single kanji, 西. In some way or other check that out >> 1一 , 2二, 3三, 4四, 5五, 6六, 7七, 8八, 9九, 10十.
For 5 = go = 五 the left side in 口 is moved to right slightly and raised to touch the ceiling. Better reasoning is the line from the ceiling touching the floor and not the left side moved or raised.
For 6 = roku = 六 one puts a slight stroke on top of ceiling, perhaps motivated by the right-wards part of し present inside: 口 .
All others are evident. One thing to note as I have mentioned the day I invented this 7七. English 7 is an uplifted Japanese/Chinese 七 which is 7, and flipped upside down.
Also I had discovered how all 10-incarnations of Indian myth is actually phonetically in most cases same or close to the Japanese phonetics of the same words.
One might also note that the numbering system of Japanese has some matches eg with Indian number scheme: eg juu is 10 in Japanese and du in Indian. [which is phonetically same because dzu] The du is then rendered to dus. [zu+zu >> du-z > das/dus] You can see for 4 too: try at home.