Rei Ayanami Shrunk by Mecha Anime Girls! chapter 3 by Ninten

Piloting your dimension-hopping, size-changing mech, you land in what appears to be a post apocalyptic Japan. Flooded cities, overgrown flora and fauna everywhere, and a lack of people made it feel rather creepy.

Even more strange, you seem to be much, much smaller in this world compared to your own... Your mech's sensors indicate that it is relatively 15 cm (6 inches) tall in this dimension, making you about 2.5 centimeters tall (1 inch). You surely looked like a small toy or large bug flying through the air.

You followed your now tiny mech's sensors, looking for signs of humanity. Apparently, there seemed to be an entire human civilization... underground?

Burrowing down into the earth, you saw it; an entirely rebuilt recreation of Tokyo, now completely underground. Thousands or maybe even millions of people must have lived down here, but why? You flew down onto the windowsill of an average looking apartment building. You wondered who lived here. Seeing someone as a giant compared to you would surely be fun.

Peering in, you were surprised to see the inside of the tiny apartment was messy. Dim lighting barely illuminated the room, there was trash strewn about everywhere, and dirty unwashed clothes littered the floor.

Based on the cute school uniform hanging up, it seemed a girl lived here, which made you even more curious what she was like...