Number 1 - The old fashioned way by fulfilling these specific requirements which in fact pops up with a simple Google search, so I'll dump that below which is from here.
- Unlocking Asuka: For those of you who want to unlock everyone's favourite semi-demonic redhead, here's what to do:
- 7/3: Send Rei to school on this day, and you get the 'Asuka transfer' event.
- 11/27-12/1: 'Shinji's recovery' event.
- 12/11: Send Rei to school, and you get the 'Quarrel between husband and wife' event.
- 3/29: Rei's 'Kaworu' event.
- 02121918 0000001F (Unlock Asuka)
Now, if you have any questions or need further instructions, then please do not hesitate to ask. And lastly, here is a document which features all the other cheat codes available for the game, albeit in Japanese since that's where I found them. Have fun! See ya!