ΔE 16.1, loose: different enough that you should pick on purpose. Castellan Green is a little lighter, more saturated, warmer than IJA #27 Ao Midori iro (Blue- Green).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Castellan Green is a little lighter, more saturated, warmer than IJA #27 Ao Midori iro (Blue- Green).
The same difference applies the other way round: IJA #27 Ao Midori iro (Blue- Green) is a little darker, more muted, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See IJA #27 Ao Midori iro (Blue- Green) on the colour wheel See Castellan Green on the colour wheel
All matches: IJA #27 Ao Midori iro (Blue- Green) equivalents · Castellan Green equivalents