I agree with Naphthalene’s comment above - plus, 5 days isn’t all that long; the forum is huge, some people only log in on certain days, etc. It may just take them a bit longer to find you. You could also comment about this thread (with a link back to here) in the Master List of Book Clubs thread to get more notice.
I didn’t vote because my Japanese isn’t good enough to join, but I was curious after you posted and went and looked it up - it’s an award-winning series (I really like the artwork) so try talking it up some more, do as Nath wrote, be patient (at least a couple of weeks) and you may get more interest.
Best of luck!
P.S. You could also add another point to your poll (if possible) of “interested, but my Japanese isn’t good enough yet for a manga”