Damn, Hard mode really is hard lol, I barely won the first invasion after losing 3-5 times at the boss with all upgrades to max, but only 6k energy. I ran out of energy in the first battle but after losing the game gave me pity 3k energy or so (it only increased to 7k energy) and managed to beat it a couple of tries later. The difficulty choices are really funny lol, Hard, Easy, SLUG. Like the game insults you for choosing the lowest difficulty lol, while technically easy = normal mode, the game describes the hard mode as the intended experience. The heroine is extremely fragile and sometimes cannot one shot the mobs (so you have to spend more action points to kill). At least there is a choice of changing difficulties if things get tougher lol.
Edit: Anyways, I just checked DLSITE and found out that this game was made by the same devs that made Pregcess of Zeven. Damn what a twist, the gameplay/ game feel/ artstyle (must have hired a different artist) is so different that it seems like it was made by a different dev. To anyone hesitant to try this game here is a gist: Game = Good, Slow corruption that is properly paced (if you like quick dickening this game is not for you), gameplay is unique and fun HARD IS HARD (don't pick this if you value your sanity). Translation is pretty bad. IT IS understandable but it leaves a shitty taste in your mouth like random words being translated to fcking "fart", or the pronouns getting shat on, like a girl is referred to as a dude, or I and they are mixed, pussy is translated to a dick... You will understand the whole story though, but the translation is extremely iffy I Hope this game has a proper translation in the future that I'm willing to buy/ support the devs.