Hi! Many things can burn fiercely, but the phrase is typically reserved for passionate emotions such as hatred or love, though it can also be used to describe actual fire. Examples: "Their love for each other burned fiercely." "The hatred in his eyes burned fiercely as he looked at his enemies." "The wildfire is burning fiercely." As a combined phrase, it is usually used only in literature, but it can be used in spoken English in certain contexts. Hope this helped! Ide

It's a bit hard to know the meaning without knowing the context.

"fiercly" can also mean powerful and intense; anger need not be present from google: in a savagely violent or aggressive manner. "the army clashed fiercely with militants" in a powerful and destructive manner. "the wind was blowing fiercely" with a heartfelt and powerful intensity. "campaigners have fiercely opposed the proposals"

It's hard to understand your question.