遡河魚 （ソカギョ） anadromous fish (fish that migrates upstream, e.g. salmon)

遡及 （ソキュウ） tracing back, retroactivity

遡源 （サクゲン） returning to the origin, going back to the beginning, retracing

遡る （さかのぼる） to go upstream, to go back (in time, to origin), to date back to, to trace back to, to make retroactive