Board Thread:Beginning Singers/@comment-59.189.112.160-20150704040033/@comment-5290733-20150707004415

73.140.150.231 wrote: If...an actual  instrumental was released I think it's fine

It's only fine if the official released instrumental was released publicly for free. If it's part of a CD or something, then yeah, some people can cover it and get away with it because the anime company doesn't care, but usually it will result in a copyright strike and audio takedown.