Where does “ば行” come from?

ば行 (Japanese) comes from Japanese ば, from Japanese は, from Old Japanese は.

ば行 (Japanese): a row derived from the は行 of the 五十音図 (but not included in the table) by adding the diacritical mark ゛, consisting of the five kana ば/バ, び/ビ, ぶ/ブ, べ/ベ and ぼ/ボ

Definitions

a row derived from the は行 of the 五十音図 (but not included in the table) by adding the diacritical mark ゛, consisting of the five kana ば/バ, び/ビ, ぶ/ブ, べ/ベ and ぼ/ボ

Ancestry of “ば行”, step by step

ば行 traces back through two separate lines of ancestry.

via Japanese ば

Step	Language	Word	Meaning
1	Japanese	ば	In Modern Japanese, attaches to the kateikei, and...
2	Japanese	は	what about, where is; Inserted between two verbs...
3	Old Japanese	は	—

via Japanese 行

Step	Language	Word	Meaning
1	Japanese	行	a line of text; a row of a matrix; Abbreviation...
2	Middle Chinese	行	—

Every word from Old Japanese は →Every word from Japanese は →Every word from Japanese ば →