Where is the CG picture?

[Mk51]

I recently started playing this game. After reading the guide on achievements, I had a problem. When will the menu with CG pictures open? I already killed 1 boss, saw a cutscene in the bathroom with Kizmel, saw a cutscene on the lake with Asuna and Yuuki, and the relationship with all the characters except Premier and Kizmel 6+. But there are no pictures! What am I doing wrong? Thanks.

[-BritishEcho-]

You unlock the gallery when you complete the main story.