The show's portrayal of time travel looks gripping to say the least!
As a disclaimer, I've not seen any of the episodes. But I did take a look at the video you mentioned here. There are satanic elements to the dialogue, for example here: "Only when we're free of all emotion are we truly free. Only when one is ready to sacrifice what one holds dearest." To be ready to sacrifice whatever one holds dearest to me sounds incredibly dark given the context of some of the scenes in the tribute. I've come across the displeasure of reading online of a satanic ritual where one kills his/her dog after cultivating a bond with him/her. The supposed idea is to take the life of someone who sees you with love, similar to that of a child. The satanic person and the dog feel that love and to break that bond so brutally requires that they free themselves from that positive emotion.
I'd imagine there's much more graceful ways of letting someone go, and concerning emotions, they are integral to learning and the path towards STO.
Again, I've not seen the show so please correct me if I'm wrong. As with anything it would be wise to practice vigilance and to practice awareness in the essences that you may encounter in the show.
You aren't wrong.
However, religion per se doesn't really feature in the show but the setting is one where people are mostly driven by pain or desire i.e. driven by their emotions.
One of the main characters see's that the world has nothing but endless suffering and people repeat the same patterns over and over again, patterns which lead to theirs and others suffering and from this, he wishes to destroy the world i.e. he strives for non-existence. The character in question has grown old and weary, he's weighed down by a lifetime of being unable to escape the darkness of suffering as it were. In this sense, he adopts pretty nihilistic views, I think you can call them satanical views? (Though again, worth mentioning religion doesn't really feature).
The show isn't a feel good show. I wouldn't say it's a depressing one either but the editorial and filming style is a sombre one, it's a reflective one - colours aren't necessarily bright, things are somewhat grey, cloudy, slightly dark in appearance. The style is one which has been employed in other shows, usually detective type shows or gritty type shows / movies like the Dark Knight series starting Christian Bale - you get the drift.
The show unlike a lot of modern ones isn't really violent or explicit in language or sexual scenes though there are minor moments. It's more about dialogue and contemplation as the basis for the drama.
At least that was my take!