No worries, the two times where it comes up use it for emotional poignancy.
(Xenoblade Chronicles Spoilers)
There's a heart to heart where he mention hearing the ghosts of Shulk's parents at Ose Tower, and the other time is actually in the main story when he hears Kallian's final words to Melia before passing on, and Melia is touched when he asks where he is, because Riki can't see Kallian. He does not like ghosts, but I wouldn't say he's afraid of them (before he realizes that the ghosts are Shulk's parents he tells Dunban to leave Riki to fight them off because he can't sense them).
Re: da
(Xenoblade Chronicles Spoilers)
There's a heart to heart where he mention hearing the ghosts of Shulk's parents at Ose Tower, and the other time is actually in the main story when he hears Kallian's final words to Melia before passing on, and Melia is touched when he asks where he is, because Riki can't see Kallian. He does not like ghosts, but I wouldn't say he's afraid of them (before he realizes that the ghosts are Shulk's parents he tells Dunban to leave Riki to fight them off because he can't sense them).