A bit spoilery from the point I'm at with the fic reboot, but Tsume ends up transferred from Saffron to Cherrygrove. With Donor becoming a crossover between Pokemon and Roadside Picnic, the lore follows that each Pokemon region is in itself a separate exclusion zone. Understandably he and Suri lose contact for a long time since they're stationed in two different zones.

His starter was a Drowzee, so you can understand why he'd sympathize a bit more closely with the Slowpoke Well incident considering it's also a Psychic-type. He adopted one.

I don't remember why he has the Wooper or Hoppip, but I had a reason for it. o_O