Can I get a Kansai Area Pass?

Hi!

I'll be traveling to Japan for the first time in December-January and have been researching as much as I can about the different travel passes.

I will be traveling in Japan for 25 nights, starting in Tokyo and ending in Wakayama (flying out from Osaka). I plan to purchase a 21-day JR Pass which should cover me for the majority of the trip, but as my last four days in Japan will be spent in Osaka, Mt Koya and Wakayama, should I purchase the Kansai Area Pass for these four days? If so, can this be collected from Narita airport when I first land in Tokyo?

Any help would be truly appreciated! Thank you.

as my last four days in Japan will be spent in Osaka, Mt Koya and Wakayama, should I purchase the Kansai Area Pass for these four days?

If you mean Wakayama city, then the Kansai Area Pass is not appropriate. Koyasan is not covered by (JR's) Kansai Area Pass. You might better consider Kansai Thru Pass which is valid for non-JR trains/buses in Kansai area including Osaka, Koyasan and Wakayama city.

https://www.surutto.com/tickets/kansai_thru_english.html

BTW, 21 day JR pass is not cheap, so you might better calculate your train travel. Sometimes it is cheaper to buy individual tickets and even flights are cheaper/faster.