I'm going to lay out a wild guess here:
I'm presuming (arbitrarily, admittedly) the -HI is probably not part of a 5-syllable name/surname, and obviously the preceding letter isn't -S. Also, I can't really think of any names/surnames that end with -HI, though that's just me. Since this character is probably Japanese, and the author of this work is a Japanese man, I'm going to assume the first four syllables are his surname. I'm going to assume, then, that his given name has four syllables and begins with -HI. Possibly...Hideaki?