Arcana Heart 3

To get this achievement, you have to unlock all illustrations in VISUAL page of the GALLERY. There are many things you have to do for this, but among others, you must finish the story mode with every 23 playable characters. So this guide assumes that you've done that, and mainly explain things that you might miss in that process.

The VISUAL page of gallery can be divided into several sections, and we're going to cover each section. In the following guide, notations like "R1C1" means the position "row 1, column 1" in the list.

Section 1: Character visuals (from R1C1 to R5C4)
Most visuals of this section are unlocked by simply playing that character. Some special cases are,
R2C6: Mildred: Unlocked by choosing Mildred: the Halo as Arcana.
R5C2: Broadcaster Hyohdoh: Unlocked by finishing the story mode (might be unlockable by just playing earlier stages of that mode).
R5C3: Dr. Ming-Fang: Unlocked by finishing the story mode of Mei-Fang.
R5C4: Ragnarok: Unlocked by finishing the story mode (presumably).

Section 2: Character cutscenes (from R5C5 to R10C4)
Visuals on this section are usually unlocked by performing that character's super move or Critical Heart. Some cases that call for special attention are,
R6C3 to R6C5: Cutscenes for super moves of Kasuga sisters. You might need to perform a specific super move of Maori to unlock these.
R7C6: Mildred: Presumably, Mildred's Arcana Blaze unlocks this.
R8C5: Clarice 1: Clarice's super move.
R8C6: Clarice 2: Clarice's Critical Heart.
R9C1: Chromachias: Some super move of Clarice.
R9C6: Parace L'sia: The final boss of score attack mode. If I remember right, you don't have to defeat her to unlock this. You just have to see perform her super move, and that will almost certainly happen in the fight with her.
R10C1: Scharlachrot 1 : Scharlachrot's super move.
R10C2: Scharlachrot 2 : Scharlachrot's Critical Heart.

Section 3: Arcana visuals (from R10C5 to R14C3)
These visuals are simply unlocked by choosing that Arcana as your partner.

Section 4: Movies (from R14C4 to R14C6)
R14C14: Opening movie: Available from the beginning.
R14C15,C16: Staff rolls: Presumably unlocked after finishing the story mode.

Section 5: Story mode visuals (from R15C1 to R15C6)
Unlocks in the course of story mode. R15C3 might only be unlockable in Scharlachrot's story.

Section 6: Story mode endings (from R16C1 to R21C3)
These visuals are unlocked by viewing each character's ending in story mode, the hardest part of this achievement

Section 7: Specials (from R21C4 to R24C1)
The first two visuals of this section are available from the beginning. But the remaining 14 can be a bother. As far as I know now, no definite way is known to unlock these. It is said that playing with the characters (or Arcanas) depicted in the visual for a certain number of times or a certain amount of time, will have a good chance of unlocking that visual. It also seems that sometimes (or rarely) it unlocks just randomly.

I strongly recommend to put off this section. You can check this after you've finished all other sections and all link animes. Anyway, the list goes.

Special CG #01: Weiß and Heart.
Special CG #02: Kayatsuhime: the Flower (Arcana) and Partinias: the Love (Arcana)
Special CG #03: Fiona and Saki.
Special CG #04: Dorothy.
Special CG #05: Weiß and Gottfried: the Tyr (Arcana)
Special CG #06: Angelia
Special CG #07: Lieselotte and Zenia
Special CG #08: Kasuga sisters (i.e. Maori).
Special CG #09: Petra, Elsa and Clarice.
Special CG #10: Kira and Catherine.
Special CG #11: Akane, Nazuna and Konoha
Special CG #12: Lilica and Yoriko
Special CG #13: Mei-Fang and Kamui
Special CG #14: Scharlachrot and Eko