- かい: full gentler variant of question particle か (ka), used by some men.
According to my sources that seems incorrect. kai is not gentler. It is infact indicating that a posisive response is required, when a superior speaks to a subordinate (for example). Wakarukai would mean something like "You get it, don't you?". This was according to my Japanese friends. Does anyone have anything coming out of a grammar book? :)