Listen new single of ukrainian dark metal band Tectum feat. a capella female band Budnitay
[artist]Tectum[/artist] - [artist][track artist=Tectum]Shchedryk (Carol of the Bells) feat. Budnitay[/track][/artist]
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Sound Horizon also has a great operatic sound while also containing metal influences. Plus their albums (especially their most recent one) are closer to programmatic music and actual operas/plays than most of the other bands listed here.