The issue was why use Onyomi here in the first place. Googling it is showing more hits for ι£γγ»ι£γ than I'd expected, though ι£γΉγ is obviously far more common.
Obviously ι£γΉγ has more widespread use, but that doesn't make ι£γγ any less of a legitimate word. Literally meaning "to do food," it's just a more casual way of saying "to eat" as far as I can tell. Just as in English you might say "I'm going to eat" or "I'm going to grab some food" or "I'm going to have some grub" or "I'm going to chow down" etc.
Actually, my feeling for ι£γ is archaic/formal rather than casual. ι£γ(kuu) would be casual though. I'm writing this one off as a failed attempt by the artist to add depth to the dialogue that would be indicative of Rider's background / speech style. ι£γζΉ is really unnatural sounding.