Oricon weekly results (rank, sales):
16 13,345
61 3,387
102 1,845
120 1,753
121 1,642
As you can see the sales dropped after the first two weeks. Then it stays at about the same level, only losing about 100 every week. If this continues Mitsuboshi can stay in the album top 300 for quite some time. It will be interesting to see if this album can indeed withstand the general trend of diminishing CD sales.