When discussing anime like Pokémon and Sailor Moon, many fans will argue both of them highlight those with magical powers who make use of friendship. Comparing characters like Sailor Moon and Ash Ketchum is probably not ideal from the power level standpoint, but investigating both from a psychological perspective can take the weight.
Diancie can be a Pokémon that may create diamonds, hold its very own against powerful legendary Shiny 6IV Pokemon like Yveltal, and transform right into a stunning and delightful form that packs a punch. Diancie's powerful moves, Meteor Storm and Misty Explosion - can come in handy to Sailor Moon since Diancie's Fairy typing is super effective against dark, dragon-type powers.
Sylveon's majestic appearance and cuddly persona ensure it is an adorable Pokémon many want on their team. With attacks like Moonblast and Dazzling Gleam, dark entities wouldn't like to seek a grapple with this creature. Sailor Moon would commend Sylveon for his or her efforts and strength and would like to have another cat-like pal at her side. Having a Pokémon that will defeat the evil in an offensive and passive way sounds more aligned to Sailor Moon's justice methods.
Delcatty's eagerness to stop danger may impact Sailor Moon's reasoning not to resorting to violence to Shiny Pokemon Buy and get rid of specific conflicts. Not only that, but Delcatty generally is a Pokémon Sailor Moon can offer around when she's feeling down. Not to mention that Delcatty's fur adored by many trainers inside the Pokémon world, and yes it wouldn't be odd for Sailor Moon to wish a warm creature to cuddle with sometimes.
When fighting evil by Moonlight, Sailor Moon may need time to relax and relish the wonders of life around her. A Pokémon that will bring Sailor Moon a wish that way could be Togekiss since its elegant appearance and majestic nature aren't the sole traits it offers. From their kid-friendly days as being a Togepi for their soaring days being a Togekiss, bulbapedia claims trainers seek Togekiss with the luck they're able to bring to them.