Does anyone know what this song is?

[UlquiorraKuchiki]

its the song that starts playing when Grimmjaw begins to release his zanpaktou in ep.166. its also in the battle scene in ep.168 when they begin to fight the menos.

[HanakoAbarai]

there is probably no way of telling now, as the OST for the HM arc will be released once it's over. Then you will be able to find its name and you'll probably find it available on bleachexile anyway...