When you were the most bored, you traveled through time, hehe.
You were about to play in the new world, but you were eaten by a giant that suddenly appeared. No hehe.
In the smelly belly of the giant, your consciousness is invaded by Sanwu Advertisement, which throws out two options:
A: Transform into an Innocent Titan and give experience points to the protagonist group.
B: Become the brick guardian protagonist group on Maria's wall
You: ... Protagonist group? Do you mean to use me as cannon fodder?
Mission: Prosperity, Democracy, Civilization and Harmony