Dear Hadi,
Dear Reader,
It's a positive sign that you are concerned enough about this issue to ask whether something you find entertaining is something you should continue to watch. From an Islamic perspective, we believe the answer is not necessarily a simple “halal” or “haram." The important question is what the content contains, how you are affected by it, and whether watching it causes you to compromise your obligations and values as a Muslim.
If a show contains nudity, sexual content, glorification of sin, mockery of Allah or religion, or other material that you know you should not be looking at, then you should avoid those scenes. Allah SWT commands believers to lower their gaze and protect themselves from what harms their faith. If you can skip or avoid inappropriate content, that is better than deliberately watching it.
At the same time, fictional representations of supernatural beings or evil forces are not automatically “satanic” in the religious sense. A fictional character resembling a demon, god, spirit, or other supernatural figure does not mean that watching the story is worshipping or endorsing that being. What matters is whether the content causes you to believe in falsehood, glorify shirk, mock Islam, or negatively affect your beliefs and worship.
It is also understandable that a story can make someone reflect on death, loneliness, suffering, the value of life, and their dependence on Allah SWT. However, we should be careful not to say that a piece of entertainment itself has strengthened our relationship with Allah without also considering whether the overall content brings us closer to obedience or gradually makes sinful material feel normal. A good lesson can sometimes be found in something that is not entirely good, but that does not necessarily make all of its content permissible.
A useful principle is: take what benefits you, leave what harms your faith, and do not make entertainment a justification for repeatedly exposing yourself to what you know is impermissible. If the questionable content is occasional and can genuinely be skipped, and the show does not undermine your beliefs or cause you to neglect your religious duties, then the matter may be different from deliberately seeking out explicit or spiritually harmful entertainment.
You should also ask yourself honestly: After watching this, am I more mindful of Allah SWT, or am I becoming desensitized to things I previously knew were wrong? Do I skip the inappropriate parts, or do I use the good messages to justify watching everything? Your conscience and your relationship with Allah matter here.
We are not familiar with the specific content of this anime series, but ultimately, if you are unsure about particular scenes or themes, ask a knowledgeable and trustworthy scholar who can assess the specific content rather than issuing a ruling based insufficient information. And remember that leaving something doubtful for the sake of Allah SWT is never a loss. There are many forms of entertainment and storytelling that can provide meaningful lessons without putting you in the position of repeatedly wrestling with questionable content.
In peace.