In the show, it shows Shougo actually slashing at his master and blinding him in a flashback. So, it's not just something like reflecting moonlight off a sword. However, it should be noted that in all instances he used the Rai Ryu Sen, he did require some form of ultra bright light in the darkness to use it. So, if the OP wants to stipulate that it's night, it's possible for him to use it.. otherwise, I don't think it'd be wise to use that as his winning hand.
;_;...@Christian arc. That was a truly good arc, despite it being a filler one. Shougo was a really well written character, IMO.