Gigant

Gigant (ギガント, Giganto) is a Japanese manga series written and illustrated by Hiroya Oku.

Plot
Rei dreams of becoming a big-ticket film director, but when he stumbles into a chance meeting with a busty adult film star, his high school life takes a turn for the strange. Not only does his favorite porn star like him, she gains the power to grow to an enormous, towering size! Is alien technology to blame? Time travel? The end of the world? All manner of bizarre trouble lies ahead, and a gigantic, gorgeous woman is just the tip of the iceberg!