Tsuna Codes?

[tmcroan]

What's with the tsuna codes?
All I know is they are key items with two-digit numbers as the description. I assume they come from the Tsunamod pack.
Anyways, I cant find any info on them and with out them I cannot leave Midgar after the highway boss fight. The game prompts you to give all four codes, but I've only three of them..

[Bonez]

This is part of the Echo-s Demo... If you find all 4 secret codes in the game, you get an extended demo up to Junon. Otherwise the demo ends at Midgar.