Katakana were developed as a reading help for Chinese texts imported into Japan, by taking parts of kanji with the desired reading. I found a list of these kanji in the book The Key to Kanji and figured that it might help to remember the reading of a bunch of kanji, so enjoy. [For some kana it is not so obvious which parts were taken, though.]
ワ 和 (9)
A few kanji are missing from WK, so some the reading actually doesn’t fit, but I’m pretty sure I picked the right ones.