Hououin

Attack on Titan (literally translated as "Advancing Giants") is a Japanese manga series, and now an anime, originally written and illustrated by Hajime Isayama. The story centers around the lives of Eren Yeager, his adoptive sister Mikasa Ackerman, and their friend Armin Arlert, who live in a world where the remnants of the human population live inside cities surrounded by enormous walls due to the sudden appearance of the Titans, gigantic humanoid creatures who devour humans seemingly without reason.

Rintaro Okabe is a self-proclaimed "mad scientist" who believes that an international scientific organization named SERN is conspiring to reshape the world according to its own interests. He and his friend Itaru Hashida inadvertently create a gadget able to send messages to the past.