Ichikawa did a good job at making an ambiguous test. Usually a red (or pink) line means pregnant, even if it’s very, very faint. The issue is Fubuki’s test doesn’t have pigment. It’s probably an evap line, which form once the test dries out. Basically, a little bit of the ink passing through gets caught on the indentation, then the evaporating urine makes it visible on the surface. It won’t have a color because the non-existent pregnancy enzymes don’t activate the pigment. This is why it’s good to check the results within 5 minutes! If you don’t, it might dry out and look like this.
Still, it’s ambiguous enough I’d recommend Fubuki test again, even if it’s only for peace of mind. You can buy strips in bulk pretty cheap. (Maybe ten cents each test, but Japan might be different.)