Niko is a masculine name, the Finnish form of Nicholas which means “victory of the people” from Greek Nikolaos. It’s also the Croatian and Slovene short form of Nikola, the Slavic form of Nicholas. However, Niko can also be used as a short form of Nicholas or its’ feminine forms Nicole and Nicolette, making it a unisex name.
Niko also seems to have a Japanese origin but I couldn’t find anything concrete behind it or the meaning. If anyone knows more about it, please let me know 🙂