Left: "Yu~ Yu~ Take it easy with the cute Reimu and her little ones~ (no idea what the heck piyan means)"
right: Yukkuris have many things you need to drill into them as a pet, such as "don't be noisy", "listen when you're spoken to" [rest omitted]. Compared to toy dogs or toy cats, they have many minus points.
So in order to get rid of these minus points, we have manipulated the inheritance-bean paste and have successfully removed those problems! These are "very easy" little Reimus!
"yu-pyan" is one of those made-up, obnoxiously cute things said by obnoxiously cute characters. You see this all the time with young pop idols in Japan, or as verbal tics for super-cutesy characters (e.g. in Di Gi Charat).