isn't 7 nana?
also, isn't 6 roku not ro?
There are multiple puns for each number , is not as straight forward as a combination of Ichi , ni , san ,shi,go,roku,nana ,hachi, kyu
If you look in the description of his videos you can find a reference page to the puns , i will copy paste what i got from there using google translate
0
Rei, Re, Zero,Nai,Wa, Maru, Ma, Ou, A, no
1
Ichi,I, Hitotsu, hito, hi,Ai, bo,Ma
2
Ni,futatsu, futa,fu, Butsu,bu,ji,pu ,putsu
3
San,sa,mittsu,mitsu,mi
4
Yon,yo,yottsu,yotsu,shi, fu-o(dall inglese)
ho
5
Go, ko,itsutsu, itsu
6
Roku, ro,mdutsu,mu,riku
7
Shichi, nanatsu,na
8
hachi,ha,pa,yatsu,ya
9
Kyu,ki-yu,ku,koko,ko
10
ten, to , do,jo
CHINESE
0 Rin
1 E
2 Al
3 San
4 Su
5 U
6 Ri-u
7 Chi
8 Ba
9 Ji-u
10 Shi