So I had some competing theories pre Kanji kidnapping. 1a) Mayumi Yamano (first victim) had some unknown connection two Yukiko and Saki. 1b) This was just a random misogynistic serial kidnapper who hates women.
Post Kanji I had to exclude 1b) so I moved on to theory 2a) Kidnapper is targeting prominent people in Inaba, possibly with a connection to Junes moving into the local economy (though Mayumi and Saki were somewhat mutually exclusive in either case). Theory 2b) was a refinement on 1b - the kidnapper is targeting women AND gay/bi men. Mitsuo I knew was a red herring but that was meta knowledge from knowing that other persona games don't end in the summer.
Rise and Nauto's kidnappings