Reasons why to watch the first season:
1. Learn about the Heaven and Hell's Gate and how they are linked and why the walls were built around them.
2. What the meteor core and a little bit about its power (it might give you a little insite on why everone is searching for it in season two.)
3. Learn about what the Tokyo Explotion is, who caused it, and why. (The Tokyo explotion is linked to the second season.)
4. Why Contractors are rational thinkers and how it effects their emotions. (It will give you insite on why Suou's brother used her as a decoy.)
5. Why Hei is special, when he got his powers, and how he got the name "Black Reaper."
6. What are Dolls, what they are for, and how they are created.
7. Who is Bai/if that is brought up.
8. Who that female is at the end of s2 ep 2.
9. Who Mao is and why he is believed (at this point) to be in the squirrel.
10. And it's just too awesome not to watch.
And please don't say you don't care about any of that. Let the person read the list for themselves and make the decision if it will be worth watching.