User blog comment:Xilinoc/Ch. 565 (Mangapanda is run by lazy barnacles)/@comment-1351982-20140122164702/@comment-5847836-20140123041620

The Tetragrammaton יהוה "YHWH" ends in the letter ה (he), the [h] of Hebrew.

The English forms Yahweh or Yehowah have the same final fricative.

Allowing for terminal vowel reduction, ユーハバッハ "Yuhabahha" approximates the form Yehowah, again with the same final fricative.

Note that the transliteration "Jehovah" is Latin, and therefore is pronounced "yay-hoe-wah," not "jeh-hoe-vah" as many English speakers incorrectly do.

As the Quincy are German, the "ch" in Yhwach is not the [k] of English, but the  [x] (very soft ch) or ach-Laut of German (as opposed to the  [ç] ich-Laut – "ch" is pronounced differently for different vowels in German). To an English speaker, it sounds almost identical to [h].

The same is seen in the German pronunciation of Bach: much closer to "Bah" than to "Bock."

So Kubo is using "ch" correctly – not a matter of Hebrew, but of German orthography.