#!/bin/bash

find "$PWD" -type f -name '*webp' -print0 | \
    while IFS= read -r -d '' file; do
        newfile=$( echo "$file" | sed -r "s|nhentai_[0-9]+_0||g; s|\.webp$|.png|")
        printf '%s ---> %s\n' "$file" "$newfile"
        magick "$file" "$newfile" && rm -f "$file"
    done