Translation

The Japanese word for "Mule" is raba ラバ.

Romaji ra ba
Hiragana
Katakana
Kanji
Meaning Mule Horse
School Level 小2

Loan-word

The word "Mule" katakanized would be myūru ミュール.
Romaji myuu ru
Katakanaミュ
Hiraganaみゅ

Further Reading

Wikipedia: Mule (騾馬)