Can I reserve a seat if I buy one way ticket and not the JR PASS?

We are traveling to different cities in Japan in a three week journey, starting from OSAKA-KANSAI to Hiroshima, then Okayama, Kurahiski, Takamatsu-Kagawa, Osaka, Kyoto, Kanazawa, Shirakawa-go, Tokyo and day trips out of Tokyo. When we budget costs of buying separate ticket prices is cheaper than acquiring the JR PASS. My only concern is: can we reserve seats even if we do not buy JR PASS? Thanks