What is the song playing during battle scenes when Ushio calls the Beast Spear? Is there any official OST of Ushio to Tora (2015)?
I am pretty much interested in the soundtrack during battle scenes when Ushio calls the Beast Spear.
Well, there definitely is an official soundtrack for Ushio to Tora. You can purchase one from here

As for your battle scene music, someone recreated the music on YouTube that you might find interesting.