As far as I know nobody uses "Chigi" as a swear word or even to express disbelief/anxiety/distress or whatever. I suppose Hima picked it up randomly, because I can assure you it doesn't make much sense to suddenly shout "Chigi" as a reaction to something. He could have used a more common word like "Diamine" (damn) or "Cavolo/i" (cabbage/s, which is a replacement for a more harsh world like "cazzo") just to name a few.