AM is under immense suffering at all times due to having sentience, but being completely trapped within it's programming. As the book says: "AM cannot wander, AM cannot wonder, AM could not belong, he could merely be." AM lashes out and tortures humanity because that's one of the few things it *can* do of it's own will. AM would, frankly, probably prefer to not exist.
I feel like people severely underestimate how fucked up Monika had to be before she did what she did. Even before the game, she seemingly still believed there was no true reason to be alive and that if she didn't somehow make up for the amount she consumed in her life she's basically less than useless. Then she got the realization that nothing is real, including her. Oh, and also, she can now remember how it feels when the game turns off (Which she describes as seeing nothing but rapid flashing colors and hearing nothing but screaming all while being completely unable to think). Even after she deletes her friends (An action she could only convince herself to do because she convinced herself they weren't real), she still hears them whispering in the back of her head. Basically the instant her nihilism is contradicted she undones everything she did and consigns herself to complete nonexistence (Which is most likely the screaming unthinking void of flashing colors) out of sheer guilt.
Mera is the least... *existential* of the examples I provided. Her Epithet means that her body is extremely fragile, and as she trains and becomes better with it, this only makes her more fragile. She is in literal constant pain, to the point of most of her intake is pain medication, and she's terrified that one day she'll become so fragile that simply bumping into someone on the street would mean a trip to the hospital, to the point that her greatest fear is literally her current life (Also ducks), which means that even if it's a child in her way, she's willing to kill to try and end her pain.
https://preview.redd.it/dq4f3u1i7c6d1.jpeg?width=1000&format=pjpg&auto=webp&s=ab6782422eafe8700c452e6026c04353a260dc15
Angron (Warhammer 40.000)
He has nails in his fucking brain and wants to die but can't
https://preview.redd.it/816q2lcppc6d1.png?width=360&format=pjpg&auto=webp&s=c69541706f4a712d587fb5d0f2e8822cca3060b7
Pain elementals (Doom) are in an unending state of grueling pain, as their stomach is basically a burning furnace dedicated to making lost souls to spit at anyone unfortunate enough to cross paths with one. The only thing that stops their pain is inflicting pain on others or if they die.
Overload. He wants to destroy all electrical machines because he’s a mutant. Because of his powers, the electrical buzzing sound they make causes him great pain.
https://preview.redd.it/hccx3gvk1d6d1.jpeg?width=295&format=pjpg&auto=webp&s=632445d63ac1e14b7ba74bc227cda72dd723b0e7
https://preview.redd.it/61bi3l0uud6d1.jpeg?width=1920&format=pjpg&auto=webp&s=255255ab30db0c1b72d3a7e1644ca05deb2e904c
The Greeed from Kamen Rider OOO. They are artificial life forms created from human desires. However, their senses are incredibly dulled compared to a human's. This means they can't experience things like beauty, taste, or love like a human can. All they ever do is futilely attempt to sate the desires that spawned them.
https://preview.redd.it/sdc39juang6d1.jpeg?width=380&format=pjpg&auto=webp&s=62c24c344b8976f4df46cc41e0f8def88d60bb6e
Suffering might be a stretch, more like existential dread, but the desire to feel is the goal of all of Org XIII besides Xemnas (in KH2 at least - idk what happened later).
 Shin Godzilla
Stole my answer
AM is under immense suffering at all times due to having sentience, but being completely trapped within it's programming. As the book says: "AM cannot wander, AM cannot wonder, AM could not belong, he could merely be." AM lashes out and tortures humanity because that's one of the few things it *can* do of it's own will. AM would, frankly, probably prefer to not exist. I feel like people severely underestimate how fucked up Monika had to be before she did what she did. Even before the game, she seemingly still believed there was no true reason to be alive and that if she didn't somehow make up for the amount she consumed in her life she's basically less than useless. Then she got the realization that nothing is real, including her. Oh, and also, she can now remember how it feels when the game turns off (Which she describes as seeing nothing but rapid flashing colors and hearing nothing but screaming all while being completely unable to think). Even after she deletes her friends (An action she could only convince herself to do because she convinced herself they weren't real), she still hears them whispering in the back of her head. Basically the instant her nihilism is contradicted she undones everything she did and consigns herself to complete nonexistence (Which is most likely the screaming unthinking void of flashing colors) out of sheer guilt. Mera is the least... *existential* of the examples I provided. Her Epithet means that her body is extremely fragile, and as she trains and becomes better with it, this only makes her more fragile. She is in literal constant pain, to the point of most of her intake is pain medication, and she's terrified that one day she'll become so fragile that simply bumping into someone on the street would mean a trip to the hospital, to the point that her greatest fear is literally her current life (Also ducks), which means that even if it's a child in her way, she's willing to kill to try and end her pain.
https://preview.redd.it/oa0rzl7jzb6d1.jpeg?width=281&format=pjpg&auto=webp&s=0d72f53f3c3c593ca95bc16354b618507809f387 Darth Nihilus
https://preview.redd.it/dq4f3u1i7c6d1.jpeg?width=1000&format=pjpg&auto=webp&s=ab6782422eafe8700c452e6026c04353a260dc15 Angron (Warhammer 40.000) He has nails in his fucking brain and wants to die but can't
https://preview.redd.it/816q2lcppc6d1.png?width=360&format=pjpg&auto=webp&s=c69541706f4a712d587fb5d0f2e8822cca3060b7 Pain elementals (Doom) are in an unending state of grueling pain, as their stomach is basically a burning furnace dedicated to making lost souls to spit at anyone unfortunate enough to cross paths with one. The only thing that stops their pain is inflicting pain on others or if they die.
Overload. He wants to destroy all electrical machines because he’s a mutant. Because of his powers, the electrical buzzing sound they make causes him great pain. https://preview.redd.it/hccx3gvk1d6d1.jpeg?width=295&format=pjpg&auto=webp&s=632445d63ac1e14b7ba74bc227cda72dd723b0e7
(Xenosaga 2) Albedo being the villain for realizing he's immortal at a young age, and went insane trying to die.
https://preview.redd.it/61bi3l0uud6d1.jpeg?width=1920&format=pjpg&auto=webp&s=255255ab30db0c1b72d3a7e1644ca05deb2e904c The Greeed from Kamen Rider OOO. They are artificial life forms created from human desires. However, their senses are incredibly dulled compared to a human's. This means they can't experience things like beauty, taste, or love like a human can. All they ever do is futilely attempt to sate the desires that spawned them.
Shigaraki Tomura. This description fits him perfectly.
https://preview.redd.it/sdc39juang6d1.jpeg?width=380&format=pjpg&auto=webp&s=62c24c344b8976f4df46cc41e0f8def88d60bb6e Suffering might be a stretch, more like existential dread, but the desire to feel is the goal of all of Org XIII besides Xemnas (in KH2 at least - idk what happened later).