Apparently Tokyo Ghoul counts as both seinen and shounen so I'll talk about it!
(Apologies in advance for how scattered this is, I tried to keep everything as short as possible
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I really like Re: despite how much it's shit on.
I think what it serves makes the story a lot more fleshed out, especially when it comes to Kaneki's personal arc as person and how he comes to terms with the traumas he's sustained.
In the OG, we see an already lost boy forced to face a damning fate, one that forced him upon a role as a protector despite he himself being as fragile (if not the MOST fragile) as everyone around him, and in the entirety of it we just watch some kid becoming more and more lost in a twisting path that eventually leads to a bleak "end" where Kaneki resigns to a fate he had likely forseen a long time ago.
In Re:, it takes that boy and tries to piece together what had been lost.
What fascinates me is the route it took with Haise being Arima's apprentice and successor, and symbolizes what I believe to be the path to absolute dark, because I think Arima symbolizes the true fate of Haise if he continued lying to himself and repressing his true identity for a false sense of righteousness that is impossible to achieve. Arima, imo, is the personfication of the red spider lillies—someone that is meant to deliver Kaneki to his damnation as a husk meant to serve as a protector of dead memories—or vague concepts of the people he had once known, who had long since lived and flourished beyond the confines of what he thought would be their stagnantion.
However, that doesn't happen, and eventually Haise returns to Kaneki, and the painted lense Haise once saw through is gone.
(IMO i think this symbolizes or implies the breakage of a fantasy world people who experienced severe trauma live in—a dissociative state where truth is blurred and only the percieved "good" shines through; or perhaps is this to symbolize how childlike Haise was in mindset, which contrasted to he depressed vision of child Kaneki who was fully aware and chained by the reality of the world? Theres so much wiggle room for ideas)
What I really liked was that when Kaneki returned, it wasn't a thing where he was happy or op and healed and bullshit like that; imo, he actually got worse in a sense where he was completely apathetic and callous. He is still fragile, but now in a different way.
As the story progresses from there, I think what truly changes or begins the "healing" is Kaneki accepting all that had happened, and forcing himself to simply become stronger. To, despite of all he's sustained, grow and bloom and become stronger, to still be capable of love and trust despite all he's been through.
Although in the end I think it's cheap to throw in babies as "yeah hes happy and healed now cuz he married Touka and now they have a family!" I think that could also be taken as "Kaneki is strong enough now to where he has opened his heart and feels conpetent enough as a person to have children with someone and love freely despite it all"
Anyway, Re I think wasn't meant to be a thing that just progresses the story, but rather Kaneki as a character, and Kaneki I believe is someone who is meant to serve as a personification of someone with trauma, how the trauma could further manifest and kill, and how at the same time it's capable of receding and becoming nothing but a scar.
In summary: FUCK RE HATERS! ALL MY HOMIES HATE RE HATERS