Here are the top ３ ways to say WHY in Japanese
1: Naze: なぜ: Why
2: Nande: なんで: Why
3: Doushite: どうして: Why
Also if you are in Kansai Region (the Southern Part of Japan where Kyoto, Osaka and Kobe are located) and speaking Kansai Dialect (Kansai-Ben) you’d say
NANDE YANE!!! なんでやね！This is saying “why” in a very surprised but kinda non-threatening way.