I know, I know, the OLD sticky needs some serious updating. Nonetheless, here are the translations of the secret reports in Days, complete with who wrote what, courtesy of Heartstation.org.

Total report authorship:
Xemnas: 4 (Days 7, 255, 322, and 35 cool
Xigbar: 5 (Days 71, 117, 256, 296, and 355)
Xaldin: 1 (Day 119)
Vexen: 1 (Day 23)
Lexaeus: 1 (Day 25)
Zexion: 2 (Days 24, 26)
Saix: 9 (Days 9, 51, 94, 150, 171, 174, 277, 298, and 356)
Axel: 20 (Days 8, 14, 22, 28, 52, 72, 74, 96, 118, 152, 172, 194, 224, 225, 276, 297, 299, 301, 353, and 357)
Demyx: 2 (Days 97, and 153)
Luxord: 2 (Days 173, and 257)
Marluxia: 1 (Day 27)
Larxene: 1 (Day 15)
Xion: 11 (Days 50, 73, 75, 95, 149, 151, 193, 300, 321, 352, and 354)

(Note, however, that Nomura says Axel has only 19 reports, and Xion 12.)

Also thanks you Heartstation, we now have an Index of sub titled cutscenes from the Japanese version of Days.