Please be as specific as possible when letting us know what is missing or incorrect. For example, say "this game's trophy difficulty should be 8/10", with a link to a website corroborating this difficulty estimate (if possible), not "this game's trophy difficulty is wrong".
This is 'The Witch and the Hundred Knight 2' DLC 'Additional BGM [Dear Metallia]'. By purchasing it, you can change the in-game BGM to 'Dear Metallia'.