mule
騾 centers on a mule, the hybrid offspring of a horse and a donkey.
騾 combines 馬 (horse) with 累, which likely contributes the sound and may relate to the idea of accumulation or burden, fitting a mule's role as a pack animal. The exact historical development is uncertain.
A horse 馬 combined with 累, which looks like a piled-up load, gives a mule: the animal that carries heavy burdens.
For ラ, imagine a mule braying a loud 'la!' as it carries its load: la -> ラ.
—
mule