If time is not a crucial factor, you may start creating your visual novel with placeholder characters (random images) and can replace them later when you find appropriate character sprites for your project :)
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yes that's what i am doing for now :) finding appropriate characters is not exactly hard but not easy either..'i have not really seen yet a sprite that fit for my main character and then there is the matter of paying . i'm willing to pay for sprites or background i want to use as long as i can afford it. i'm still thinking about characters i really need in my story and the ones i can remove . i like Keiko and Taishiro is fine too ,i will probably use them, i wish i could draw good enough to make the characters i want but i just can't , i can draw but not that good. time does not matter too i'm not in a hurry :)