Concept of double pregnancy had appeared since vol.2 (the 1st and 4th story). But I want to discuss only this story and the Lizard Girl part 2. For example, a fairy technically impregnates an OL but ends up being pregnant too. This also goes to Saki-chan, the 3rd daughter of Lizard Girl. She also gets pregnant. But overall, I don't want to think over it so hard. I only enjoy this series so far. If someone can explain about double pregnancy, it will be a little bit helpful. Thanks.