When I first downloaded Mawarine Shuu it sounded like he was possessed by a demon. Thankfully I was able to figure out the problem and I love using him now.
All you have to do is locate these 2 folders. These folders contain whisper and raspy/vocal fry(?) appends. The creator of this voicebank didn't give these appends their own aliases so UTAU accidentally uses these samples instead of the normal samples. You can either delete these folders if you are never going to use them or you can manually add suffixes. Hope this helped!