Board Thread:Fun and Games/@comment-24810520-20151204182918/@comment-5411479-20160911112547

The word  本 can mean both "book" and "origin" but in different circumstances...so "ability origin" is just an alternative take of "book of skills".

...yep, that's basically how the furigana (katakana reading aid) works. However, the furigana can only either be in katakana or hiragana, because kanji are mostly for the meaning.