First thing to mention is every single CG is defeat only, and scenes are split into two types: The art based CGs after losing and the 3D animations when you are grabbed by enemies/traps or in the nightmare realms.
I played through the game on normal difficulty and had the goal of trying to find all the scoring trophies and cosmetics, which I think the game does a good job of making an engaging goal. I did not actively go out of my way to die to see the defeat scenes. When you beat the game fully, you can unlock the full gallery so there is no need to lose to every enemy you see.
While the enemy AI is quite simple, I do like how your skills and combat is handled. You can use up to 4 different sword skills and 4 different ammo types, earning more as you progress.
I counted a total of 10 different sword skills and 13 different ammo types, which is quite a lot. I had the most fun abusing "Two Slashes" which does absurd damage if both hits land on the same enemy. The different skills are triggered by either holding or pressing the right button, and then it also changes based on whether you are moving while trying to cast the skill. It can take some getting used to, but it kept the combat interesting for me mixing and matching what I did.
Skill use is limited by the shrimps, but this wasn't much of a problem on normal difficulty since they regenerate passively and there are plenty of them during the levels. Most enemies kinda just run at you or shoot at you, so it's quite good to use the skills with movement to get some damage in quickly before they attack, or just switch to the gun for the flying enemies.
There are some nice visual design for bosses, but if playing on normal then there isn't really much difficulty, which is to be expected. Putting a turret down and running in with either the corkscrew attack or Two Slashes made quick work of most of them. I don't know how the difficulty scales on the higher difficulties, so thats something to try if you're interesting.
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This combat system combined with the fact you have a lot of movement options including the dash, jumping and also your basic attacks can keep you in the air for quite a while kept me engaged so I played through until the ending and did all the detour levels. Plus you also have the gun with ammo based on your MP, which can be upgraded with the crystals you find. The gun isn't quite as interesting because I enjoyed using Rapid Fire Bullets too much, but there are some unique ones like the shielding bullets. There are also extra "battle items" which I just stuck to the turrets since they worked quite well, especially against bosses.
I mostly appreciated the hidden trophies and cosmetics you can collect by going out of your way to find them. Some are hidden on high up places which require a bit of platforming to reach, while others require finding hidden teleporters, hitting switches or breaking some crystal blocks. It's also nice there are constant markers telling you which way to go so that it's hard to get lost. Some good customisation options too, but I didn't use this system much. You do also find a lot of red crystals but they are so plentiful that you don't really need to go that out of your way to find them all. I reached max upgrades quite easily before the final boss.
There is one level though that falling off the edge instantly kills you, and that was slightly annoying with all the moving platforms and the fact that trophies only save at checkpoints so you have to grab them again if you fall off.
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As for cgs, based on the gallery there are a total of 37 drawn versions where 28 are monsters or tentacles, and 9 of them are petrification based (so turn to stone, gold etc)
I'm not really a fan of petrification so I just ignored those cgs, but theres still a good chunk of cgs left over. This is not including the fact that enemies also grab you in the levels with their own 3d animations. I didn't count how many there are but I'd assume it's around 40, since there are a few you can't trigger yourself. As far as I could tell it's just the one looping animation per enemy or trap, and thats it unless you get defeated.
If you never get grabbed or defeated, you can still see some of the 3D scenes as there are optional "nightmare realms" where you walk through other girls subjected to those situations. You don't get anything else for going through them besides that. It's not quite as good as actually looking at the scene directly, but it is there nonetheles.
I found the gallery to be quite annoying to navigate if you want to see the 3D scenes outside of the levels themselves, as you need to load in, get grabbed by a single enemy, then leave and do it every time. Other than that though you can go through the entire game only seeing two 3d animations, which are both part of the detour levels.
The story isn't exactly anything special but Naname and Nyanko are cute so thats all you need really. That and you get to ride a flying shark, which is awesome.
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Overall I think this game is quite fun, but I wouldn't go out of my way to play this for the cgs unless you really like petrification or defeat rape.