I'm looking for manga like LIFE and vitamin where the mangaka is seemingly sadistic and spends much of the manga "torturing" the main character by having almost nothing but bad things happen to them.

Life is an especially good example. Even though shes the victim almost everyone is against her. Also, other characters in it have their own pressures and problems respectively.

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Feed your head.

The only thing I can think of is Happy! but judging from the series' descriptions, it's nowhere near as bad LIFE.