hew , Welcome to the stamp board!
We are pushing at the boundaries of my knowledge, but I'll tell you what I can discern from your scan, and then will ask for a couple of other scans.
You are correct -- it is a paid reply postal card. Off the top of my head, I *think* this is the reply portion, but I'd need to check on that to verify. (I have't really worked with these in probably 20+ years, and my language skills have faded.) We can tell that it is a paid reply card from the 3-character column of printing at the far left of the card. Those characters also tell whether it is the originating card or the reply card. That column of writing doesn't exist on 'regular' (non-reply) cards.
The earliest this card might be is 1885, when the 1-sen design type was issued. There was a slight design change in 1886, and I can't quite tell which one it is. This type of card was superceded in 1899 with a different design, and that card was then superseded by yet another type when the rate increased to 1½ sen sometime later in 1899.
So I think the year could be bracketed between 1885 and 1899.
There is someone I know who may well be able to provide more information. Anticipating the questions he might ask, is there any way you could scan an image of the back of the card? There may be date information there (in Japanese characters), or other information that could provide more context.
Also, if you look closely, there is tiny writing in the border design of the card at the bottom. The original scan is just too blurry for me to discern the writing, but that can help determine which of 2 types of cards it is.
Additionally, if you're able to scan in the postmark (preferably both instances, at the top and bottom of the card), that could be helpful, too.
In the interim, I hope this is a bit helpful in answering your question.
