In the year of 2030 the world was suddenly struck with the appearance of gates and the birth of mana in the world, resulting in the mutation of plants, animals and insect a like. As news of the phenomena spread across the globe like wildfire some people were ecstatic while others fell into deep states of fear especially the government due to the uncertainty of what was to come. The anticipation of those who thought they will get superpowers due to the mana from novels they read were sorely wrong, humans were the only living species that was not compatible with the mana, causing many to despair.
6 Months passed since the first appearance of gates and more only came, however nothing abnormal happened over these months concerning the gates. Governments across the globe mobilized all their forces to monitor these gates, and gather information as to what other changes earth has experienced. Their efforts were not fruitless as they discovered that all living things suffered a mutation turning them into wild beasts. Except one, slugs due the unique physiology instead of getting corrupted by the rampaging mana they absorbed it evolving gaining intelligence like no other species and were given unique abilities.
After some experimentation they found out that after the slugs get launched at 30km/h they transform amplifying their abilities and increasing in size capable enough to rival the rampaging beasts, and thus the slug era began.