In my opinion you just cant push people to buy your visual novel (or any kind of game) without "branding" them first (i.e: let people know about your product). This can't be done in one night, obviously. You need to plan it carefully with long-term marketing strategy. Your product does not look appealing for most of visual novel fans (I speak here because from my experience, general visual novel fans looking for something more visually appealing like nice graphic and characters, and maybe some fanservice, before anything else). I know that several visual novels sold deviates from that pattern, but it's very, very little example and it's hard to expect that from relatively unknown creator. Take a look of the example of popular visual novel and why it's sold well, and maybe you can think from that.
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Thank you for the respond. Honestly I'm not denying that I had trouble to showcase the screenshot. I mainly focus the vn on it's story rather than the art. Since I have no character images, it's difficult to showcase the art. I would understand clearly if someone passed at first glance. Right now, I am focusing on branding. It's a bit too late, but never too late, right? The vn I have right now is supposedly focus not just on it's story but it was intended for people with depression or someone struggling to move on from their life. Any idea which tags should I use for my ads other than #visualnovel #art etc?