In every single episode of BB, and even the title card itself, any letter combo that forms an element is highlighted, or at least, a single one per word. So FeLiNa forms a perfect 3 element word, which comes out to be, as I said, Iron, Lithium, Sodium. My idea is that it's supposed to be a compound, or an attempt at forming a compound between those elements. Perhaps such an attempt is supposed to be a representation of 3 different characters, and the ways the elements interact with each other in real life represent how these characters will/do react to each other in the show. I think if we had a chemist or something with knowledge of chemistry help us, we could come to understand the meaning, I would suggest starting at figuring out how Iron Lithium and Sodium interact with each other, if they can create bonds, if they react poorly with each other, etc. Good luck.