Ultraman Girls: Strange Tales

One day, after taking a handful of sleeping pills and a handful of melatonin, Lin saw a beam of light...

When Lin woke up, they discovered they had gained Ultraman Gaia's power. But when they transformed, they found they hadn't become Gaia. Instead, they had become a girl version of Gaia. Though this Gaia looked a lot like Lin, wait, wasn't this just Lin herself?!

The story is a slow burn, not a power fantasy.