Whoever developed this made a few major errors or this game is not fully complete.
Error 1: The level up skills are the same for all characters, even those who it makes no sense for.
Error 2: The archer is not playable at all, and while other characters are somewhat playable, the lack of personalized skills makes things completely unbalanced.
Error 3: The two artillery type skills are pointless, as they do little damage even when they do hit and also have little to no AOE type damage.
Error 4: The menu upgrades purchasable from dropped gold are very limited, and the developer should likely have either had a great deal more upgrades available or remove or extend the upgrade limits. The other thing the developer should have done is to make upgrades character specific with different upgrade paths for each character.
Minor problems include the lack of content for all aspects of the game.
As for what is done right. The general imagery and artwork is quite good, including the character artwork. Game-play is also pretty decent considering the lack of content and upgrades.
For the developer to fix the major errors in this game should probably take only an hour or two of planning and a day or two of implementation. As for the lack of content, the developer could have had a pretty decent game for the mere price of a week or two for additional game-play content and however much time for more art or 'scene' type content as this is an h-game. When I consider how developed the game looks with the art content, there is quite a decent amount of time invested in this game already, and such minor amount of time in comparison could have really multiplied the game-time people were willing to play.
Overall, I enjoyed playing the first character for a while, and realized that she is very OP long term and the monsters do not grow in power or HP and just in numbers. With her AOE attack, place all post unique level skills into damage +3%. Eventually you will be one-shoting pretty much every enemy as well as not needing to move around all that much.
On the other hand the lack of balance and game-play for all the other characters is very off-putting. Use the first character to get enough gold to unlock all the other characters and some upgrades then just unlock all the gallery scenes as best as you can.