okay so a sort of guide.
there are around 3 game over scenes, one for each stage.
the first one activates when you go to fight the last boss of the jungle stage while you have the parasite status (could be fetal parasite instead)
the second one you get by fighting the doomsday machine in the second stage while having the visor hack status.
the last one you get is by having activated around 4 of the recharge chairs in the third stage and then fighting the older sister mari without destroying a little floating thing in the boss room (happens before the fight), note that one of the chairs is in the previous mission and you should have the slave hack when you go to fight mari.
there are a few achievements in the game, I don't know all of them because the translation for their hints scrolls off the page.
however the ones I do know are:
clear the game
clear the game with all the fragments (they are surprisingly easy to find, just takes a bit of exploring).
purchase all the equipment from the store (there is some extra equipment you can get for having a high pollution level but you don't need to get them for this, if you are having problems buying stuff other people have left guides and instructions on earlier pages.
destroy over 200 enemies with laser Gatling or explosives
grow the the parasitic plant to maturity (to get the plant you need to get the parasite status then complete a stage to get it to the fetal parasite stage, then go to your room which will prompt some dialog and you want to cure your status which will give you the plant, the just keep feeding your plant pollution to grow it).
complete all of Hasumi, Saki and mari's missions.
and the last one I know is register all the side effects:
hypnosis (you get this from all sorts of different enemies)
entrainment (repeatedly get hypnotized without curing yourself, I think, its another one you can get easily)
parasite (have sex with the weird sort of jar shapped enemies that stick out of the ground and don't move, it's not guaranteed to give it to you on the first try)
fetal parasite (complete a stage/mission while having the parasite status)
trance (you can get this from jellyfish enemies)
tance seal (same thing as entrainment, I think)
Slime (the easiest effect to get and in some missions I would be suprised if you didn't get it)
lactating (obtained from a type of trap found in missions found on the second and third stage)
lactation addict (basically just keep letting yourself be milked)
aphrodisiac (in the second stage missions, some areas will be filled with gas caused by a certain enemy and you will get a gas guage, just let it reach the max)
Visor hack (the is a certain enemy found in the second and third stages, it will latch onto you head, simply allow it to do so)
creepy collar (given to you by the female enemy with the wip)
slave hack (can be obtained by either doing all the recharge chairs or by attempting to transform while having the creepy collar on)
thats all the the achievements I know.
if there are any specific fragments you cannot find then just message me and I will try to help.