Why are Mikasa and Levi so strong?

Related questions

1. How did Armin become a Titan?
2. Is there a season 4 of Attack on Titan?
3. Is Attack on Titan Season 3 over?
4. Who is Eren's sister?
5. How many years does Eren have left to live?
6. What Titan powers does Eren have?
7. Are Eren and Mikasa related?
8. Is Mikasa and Levi cousins?
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Tags

1. #bloodline
2. #perfect
3. #result
4. #titan
5. #because
6. #their
7. #however
8. #underground
9. #commonly
10. #ackerman
11. #trained
12. #survival
13. #could
14. #insanely
15. #strong
16. #mikasa
17. #skills
18. #known
19. #world
20. #science