Blahaj is a shark.

More specifically a stuffed shark plushie sold by IKEA.

The word supposedly means blue shark, or shark in Swedish, but I don't speak the language, so take that as you will.

Also supposedly, the shark being a rather gentle pastel blue and pink, which matches the trans flag, it became a favorite symbol within segments of the trans community, a sort of mascot. While I can't guarantee that's why it became a symbol, it is definitely popular among the trans community. Enough so that I don't know any trans people irl that don't partake in the knowledge and joke of it, and we're half a day's drive from the nearest IKEA store.

It's a fairly popular gift for trans folks that are coming out, or making a significant step in transition, or even just because.