The seat is in row ホ.
This piece is in E major.
ホ is the 5th iroha letter and note E, while ロ is the 2nd iroha letter and note B, so they are often confused as similar ordering symbols despite different positions.
Derived from the katakana character ホ, which represents the sound 'ho'. Its use as a sequence marker comes from the iroha poem ordering, and its musical note meaning is a conventional assignment in Japanese music notation.