Japanese Adjectives afterthough on

Rule:
ADJECTIVES ALWAYS END IN A DIPTHONG OR TWO VOWEL SOUNDS TOGETHER.

They can end in ai, ei, oi, ii, or ui. The adjectives ending in ei somehow came to be irregular and don't follow the nice pattern set up for us by the other vowel comination endings.

akai, kirei, aoi, utsukushii, atsui
a i u e o

adj. - final vowel + ku + naru

These are in like manner set up to become verb or d.v. if you extend them using ku after dropping the final vowel bumpo.
akakunaru - "It's getting redder", even
kirekunaru - "You're getting prettier", "It gets pretty"
atsukunaru - "Its getting hotter, aokunaru "its turning blue or its turning red" okikunaru- "It's growing larger or It's "getting bigger"