I tried making a thread with some info around a week ago, but it either hasn't been approved yet or has been rejected. This is the best I could do for now. The post will be edited if I see any new information I find. You can also turn that Skip & Skip Mode option to the second one in the Settings for the game and save the System Data.
Stop Skip Mode
<- These should have the exclusive 360 endings for Ein's route. Upon going through this route should give you many Achievements for different scenes.
SAVE before selecting a choice here during 第三章 Chapter:
「運命に立ち向かう」→「呼びかげる」 Ending A
「運命に立ち向かう」→「見つめる」 Ending B
「運命から逃げる」→「呼びかげる」 Ending A (for getting more read/select text % for this ending route)
「運命から逃げる」→「見つめる」 Ending C
Follow those for Ein's 3 Achievements, after the game is complete and System Data is saved when it askes, click the first option to confirm, Yes and reload the save via Title Screen.
<- Once Ein's Endings are done. Follow the PS2 Guide as best as you can for the other endings that have not been unlocked yet. Keep in mind that these are not 100% accurate, and choices may have a character added or missing in the choice text, or may be completely different from the 360 version. If you get different choices for the Prologue especially, just choose the top option until you're back on track, since the 360 version has added scenes. It's also best to use lots of saves for the 100.00% text, anything that isn't red for choices from what you've picked thus far. If you get any kind of ending, where it shouldn't be ending, reload from the quick save/s and try different choices to get out of the ending you're getting. Archivement in Extra in the Title selection should tell you which Endings haven't been done. This page should list them all. Doing different endings should also give you scenes you're missing too as you progress through a game.
Unlock Gun Achievements:
Repeated usage of COLT GOVERNMENT MKIV SERIES 80
Repeated usage of COLT PYTHON Magnum 4inch Model
Repeated usage of BERETTA M92FS
You'll get one of these as your 5th choice in Gun Selection progressing through the Story with the same gun. Upon getting all 3 of them, ガンマニア
will unlock along with the last unique gun you acquire.
<- I've finally figured this out on my own. I'm kind of angry at myself for not trying it sooner. Going to Gun Storage in Extra and reading each commentary for weapon should give you this, and if you've went through every ending, you should get CGコンプリート
too going through most of the weapons here. As long as you've went through multiple times, and finished a playthrough with a CG picture opening up that has Guns in it. It further tells you about Gun Storage, which is an indication that all of Gun Storage is unlocked for you to view.
<- Gun Comments, which is the next step required for the 100.00% text Achievement, ストーリーテラー
. This requires picking Guns from not using them and using them at different times, as well as changing up the 5th to 6th choice Gun. From unique Gun, to the normal Gun you were using before to unlock the unique Gun. I recommend using the 360 Route for Ein's Endings in the Prologue. That way you can get the most Gun selections from the start. A useful tip for this would be saying that chart in some kind of HTML or Spreadsheet application, and look carefully at the choice # and text that's displayed on the screen for that Gun. When you have displayed what you need, mark the cell a background color. This was very useful for me knowing which Gun and point of what Gun I've selected was done.
<- If you've followed up until now, I suggest going through with different choices as much as you can. Taking care of the Gun comments should've bumped up the read text by a few %. Any choice that's White Text you see, go through with that until the game is over. Any possible choice might change the outcome of what's displayed for read text. Another good indication is seeing what percentage the select text is at. I recommend trying different things, and note where each ending the game ends at. I was able to get this fairly easy after trying different choices with different paths and using saving / loading. Always let the game complete though and save that System Data when it asks especially. I'm sure there will be Japanese sites later on that will have more specific walkthroughs for 100.00% read text in possible choices, and some of you may want to wait until then if you wanted to save yourself time. All in all, it's pretty short if you're using Skip Mode. If you work hard at it, and don't give up. I'm sure you'll acquire it at some point.