Here is the Top 20 sci-fi Mangas to read 

1. "Akira" by Katsuhiro Otomo

   - Set in a post-apocalyptic Tokyo, it follows the story of Kaneda and Tetsuo, two friends with psychic abilities, exploring government experiments and societal collapse.

2. "Ghost in the Shell" by Masamune Shirow

   - A cyberpunk classic exploring the relationship between humans and artificial intelligence, following Major Motoko Kusanagi in a futuristic, technologically advanced world.

3. "Neon Genesis Evangelion" by Yoshiyuki Tomino

   - Blending mecha and psychological elements, this series delves into the psychological struggles of teenagers piloting giant robots to protect Earth from mysterious beings.

4. "Astro Boy" by Osamu Tezuka

   - A pioneering work in the genre, it follows the adventures of a robot boy, Astro Boy, addressing themes of artificial intelligence and human-robot relationships.

5. "Psycho-Pass" by Gen Urobuchi

   - Set in a dystopian future where a system monitors and judges citizens' mental states, it explores the ethical implications of such a society.

6. "Planetes" by Makoto Yukimura

   - Focused on space exploration and the challenges of debris cleanup in Earth's orbit, blending realistic science with engaging character stories.

7. "Knights of Sidonia" by Tsutomu Nihei

   - Following humanity's struggle for survival against mysterious extraterrestrial beings while aboard a colossal spaceship, it combines mecha and space opera elements.

8. "Parasyte" by Hitoshi Iwaaki

   - A gripping tale of an alien invasion where parasitic creatures take over human bodies, exploring themes of identity and survival.

9. "Gantz" by Hiroya Oku

     - A dark and intense series where deceased individuals are brought back to life to participate in deadly games against alien creatures, exploring themes of life, death, and morality.

10. "Eden: It's an Endless World!" by Hiroki Endo

    - A Unique narrative set in a future world dealing with political intrigue, biotechnology, and societal conflicts.

11. "Trigun" by Yasuhiro Nightow

    - Merging western and science fiction elements, it follows the travels of Vash the Stampede, a gunslinger with a mysterious past.

12. "Pluto" by Naoki Urasawa

    - A reimagining of Osamu Tezuka's "Astro Boy," exploring themes of identity, artificial intelligence, and the consequences of technological progress.

13. "Battle Angel Alita" by Yukito Kishiro

    - Following the journey of a cyborg named Alita in a dystopian future, it combines action, science fiction, and exploration of what it means to be human.

14. "Astra Lost in Space" by Kenta Shinohara

    - A space adventure where a group of students find themselves stranded in an unknown part of the universe, uncovering mysteries about their surroundings.

15. "No. 6" by Atsuko Asano

    - Set in a utopian city-state, it explores the consequences of social control and the connection between two characters amidst a larger conspiracy.

16. "Space Brothers" by Chuya Koyama

    - Following two brothers aspiring to become astronauts, it offers a realistic portrayal of space exploration and the challenges of achieving one's dreams.

17. "Bokurano: Ours" by Mohiro Kitoh

    - A dark mecha series where a group of children must pilot a giant robot to protect Earth, dealing with moral dilemmas and the consequences of their actions.

18. "Yokohama Kaidashi Kikou" by Hitoshi Ashinano

    - A serene and contemplative series set in a post-apocalyptic world, focusing on a robot named Alpha and her observations of the changing environment.

19. "Mardock Scramble" by Tow Ubukata

    - A cyberpunk tale following Rune Balot, a young girl resurrected with advanced technology, as she seeks revenge against those who harmed her.

20. "Seraphim: 266613336 Wings" by Mamoru Oshii and Satoshi Kon

    - A surreal and philosophical manga exploring the nature of reality and the interplay between science and religion.