Unwavering Determination and Resolve in Chinese / Japanese...

This can be translated as unwavering determination, unwavering resolve, or strong determination.

堅定 means unwavering, firm, steady, staunch, and/or resolute.

決心 means determination, resolve, resolution, determined, firm and resolute, or to make up one's mind.

If you want a longer version, 堅定不移的決心 is also a popular phrase with a similar meaning. Contact me if you want that instead.