Used mainly in key names and chord notation in a Japanese musical context; equivalent to the note D.
The key of this piece is D major.
ハ marks the third item in the iroha ordering system, while ニ marks the fourth, so learners can mix up their sequence positions.
ホ is the 5th kana in the iroha order and the musical note E, while ニ is the 4th kana and the note D, so the two are easy to mix up as adjacent members of the same sequence.
Derived from the second character of the iroha poem, used as an ordinal marker and later adopted for musical note naming.