Looking for a shounen/seinen manga where the main character has his face hidden at the beginning of the series. It can be like Oyasumi Punpun or Utawarerumono, where his face is hidden for the entire series, or the face can be revealed sometime earlier. But I'd want the hidden face to contribute to the plot or atmosphere of the series.

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Being alone is only lonely if you want it to be.
Staying in lucid delusion for an eternity.

I suggest you to try Kamen Teacher and Dorohedoro. Both manga had the MC's hiding their face with mask. Heck, we actually do have a Mask category, so you can always check it out.