H.H.H.O. meaning?

H.O. are the initials of Hiromi Oka (the main character), and so the extra Hs are probably just for dramatic effect. Lots of anisongs, especially from that time period, are written for the show they are featured in to put the themes or feelings of the character into music and lyrics. If there's more to the song I'd love to know, but I think that's the long and short of it.