Japanese Crackle Finish Vase with Ducks and Round Moon Shadow with Clouds

I found this vase at a Salvation Army thrift store about a month ago and when I cleaned it up, was amazed by the detail. In particular, the pale gray round shadow behind the ducks, with a meandering outline of clouds that encircles the vase. It is just a beautiful piece. It measures 12 1/4 inches tall and about 5 1/4 inches at the widest body part, just below the gold rimmed opening. Please let me know if anyone can tell me what the red characters marks on the bottom mean. Thank you in advance!