Did the plot change so much?
After v16, you could say it's all original plot.
A couple of volumes before that were also completely original, with naofumi visiting glass's world and figuring out rapthalia's family background
The rest was mostly the same, just with changes here and there, adding new characters, powers, etc
I guess it's fine then. I hate when the adapted version when off road that I basically just treat them as two different work.
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