this is my first time asking here so please let me know if something's out of formatting. I'm transcribing this short piece called [Vampurity by Shinji Iwai][1] (it's a soundtrack to one of his movies) as a mean to:

 1. learn how to transcribe
 2. analyse and try to comprehend the piece.

Here's the first 5 bars of the transcription I made:

[![enter image description here][2]][2]

My question can be subdivided in two: 

 1. is the key B minor or is it D major?
 2. irregardless of the key, why and how does the C major triad work there if C is not in the key?

Thanks guys!

  [1]: https://open.spotify.com/track/4FVVSaMNYbCVTMtdvWH05x?si=_fdvM2GtTXG5hUPbFYF_mw
  [2]: https://i.sstatic.net/m7CoS.png