Edit: Okay I went back through and checked my messages again, when I mentioned finding Tsubaki at the same time as the water coat, it wasn't the first time I found her so I was less excited, I don't think I screenshotted her or the coat directly from the results screen, because I didn't know it was rare at the time. So I do still think it was from 6-4. I'll be running it trying to find it as well now.
I had a 2nd image of obtaining Tsubaki from a 5-3 results screen that temporarily confused me, if you're wondering. For a few minutes I thought maybe I made a mistake and it dropped there instead, but I went back and noticed that when I got the coat, it wasn't my first time finding Tsubaki and that the 2nd image was me evolving her x.X I don't like giving bad information, man I wish I knew how rare it was at the time. This is really going to annoy me. I need to make sure I didn't mess up now.
There are so many places where there could have been a mistake because I didn't know the dang coats were rare to screenshot them. I didn't even mention which coat I found in my first posts because of it. The best clue I have is just my post at 128. That I hit up 6-4, then 7-1 and 7-3 right in a row is a good indication. You can see that 7-1/7-3 does have the 3 fire coat listed. I mean drops could have been changed on maps, I could have mistaken coats (Doubtful, but who knows. I remember thinking that evolving the fire starter girl would be easy since I got one of her items so soon after starting), I could have somehow got the level wrong in that post. All these problems just because I didn't know it was rare x.X I still believe it was 6-4 though or I would be running other maps instead now. That's my best clue based on my posts anyways.
I just noticed something on the wiki:
"卑弥呼の祝祭衣 5-3( 地獄への入り口 ) 伊勢風舞★4 天女の羽衣 (2/21修正)"
The 3 star fire coat item has a remark on the wiki that seems to be saying that it was altered in some way on 2/21, could the same be said for the water coat as well?