* スペル (speru): This is the most common way to spell "spell" in Japanese, referring to the act of spelling words.
* 魔法 (mahou): This means "magic" or "spell" in the sense of a magical incantation.
So, the best way to spell "spell" in hiragana depends on the context. If you're talking about spelling words, use "スペル". If you're talking about magical spells, use "魔法".