Brittany has the particularity of having two anthems- an official one that is more or less acknowledged today and a separatist one, which is rather, err, controversial.
The official anthem Brittany gave itself de facto, as a region normally can’t have national symbols, in France (though this is constantly changing), is ma bro gozh ma zadoù (oh old land of my ancestors), which tune is the same as the Welsh anthem (Hen Wlad Fy Nhadau) and which lyrics were kind of adapted from the Welsh version too, but in Breton, by François Jaffrennou in 1898.
It used to be forbidden, along with all other kinds of national symbols, but is now well-known and considered harmless. Yet, to sing it with a crowd at a gathering can sometimes be considered a political act, depending on how the whole thing was organized.
Anyway, here’s a beautiful version of it, sung by Nolwenn Leroy. Normally, it is a little slower.
And then you have La Blanche Hermine, written and composed by Giles Servat in 1970. A controversial song as it contains elements that are downright nationalistic and incites to resort to violence to obtain what one wants- in this case, to separate from the rest of France.