The Anima Effect

The Anima effect is a strange Phenomena that began effecting the human race generations ago, for some reason on their 18th birthday people transform into animal hybrid. DNA changes in minutes along with their body.

1- the effect always triggers in the day of someone’s 18th birthday, not a day sooner or later

2- it happens to EVERYONE at the point in time the universe is at the effect is a known phenomenon that affects all humans, they change at 18 there’s no if’s and’s or But’s

3- you can change gender as a result of the change

4- you may change size growing super human proportions but rarely to the level of a giantess or giant

5- hybrids even if different species are still fundamentally human and therefor capable of breeding, everyone is born human regardless (Think of it like a Butterfly's offspring being a caterpillar.)

6- what you turn into is basically random, size, gender, species it’s all out of your control, statistically you have a slightly higher chance of being the same species as a parent but there’s no garuntee

7- Myhtical or Extinct species sometimes appear, though they are rare, one in a million level incidents.

(Concept credited to ClockworkTG)