The definition of "Dysthanasia" on Wikipedia is as follows:
Dysthanasia occurs when a person who is dying has their biological life extended through technological means without regard to the person's quality of life.

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From the in-game documents, we know that the protagonist, 396-chan, actually died in a car accident. Her father, driven by desperation, utilized his company's vast resources to conduct research that eventually brought her back to life. The red medical pod that gradually grows larger and the intermittent beeping of the EKG monitor at the start of the game are clear indicators of this artificial life support.

However, the process of being "maintained" by these devices was an agonizing experience for 396-chan. This immense physical and mental suffering is personified throughout the game as the various monsters and death cutscenes. After enduring countless hardships, 396-chan finally obtains the key and approaches the medical pod. By using the key, she chooses to end the life that was being forcibly maintained.

In the final scene, when the unknown girl touches 396-chan’s forehead and the EKG monitor emits a continuous flatline tone, it signifies that 396-chan has finally been liberated from her cycle of pain. In that sense, despite its solemnity, could this be considered a "Good End"?

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The plot analysis above is just my personal speculation. Since I haven't played the developer's previous titles, this might not perfectly align with the official lore, but I believe I'm on the right track.

To experience the full content, please download and install the patch from the publisher’s official website. It takes about 8 hours to reach 100% completion.

In the current version, after installing the patch (18G version) and collecting all the Lucifer dolls, you will unlock all cutscenes and two outfits: the swimsuit and the bikini. Interestingly, if you uninstall the patch and switch back to the vanilla version, you’ll find that your doll collection progress is synced, and the two vanilla-exclusive outfits (the school uniform and the Gothic outfit) will also be unlocked.

I highly recommend this game. Honestly, it’s quite rare for a title with this specific theme to avoid being censored and make it onto Steam. The only downside is that the two outfits from the vanilla version are exclusive—it would have been perfect if the 18G version included them as well.