User blog comment:B214/DxD Queen tournament/@comment-13032946-20150209034619/@comment-93.105.240.132-20150211230342

No a main character (or protagonist) is usually only 1 so that would be Issei.

Then there are major which have lots of screen time too, sometimes as much as the main.

Next there are minor characters with low screen time yet have some relevance to the story like Lord Gremory.

Lastly there are extras who usually only appear once and often are not even named.

So if you consider Rose a main that's fine but concept wise she is not.