Got it in about 3 hours (everyone was at lv. 220+), here some tips/notes:
ATTENTION, THERE COULD BE MINOR SPOILERS (not related to the story anyway...)
- Screw sidequests, focus on the main quests.
- Every chapter will last 5/10 mins, 15 in some cases (Chapter 11 - with Zephyr SOLO last less then 2 minutes).
- All your colored hexes are gone, you cannot bring them in NG+, but there's no need to farm them (you'll get more than you need at the beginning of each chapter).
- All the terminals you placed are now gone and the whole map is blocked again, so you can't warp from any Level to the base (pretty annoying when in ch. 7 you need to reach "Mine 24" in Level 11)
- Equip the Strongman's Bangle to avoid random encounters
- In firsts Chapters (at least) equip to someone the First Aid Kit, Escape Exes will save you some mins.
- Sonic Chugs (First Aid Kit item, never used) will double your speed.
- Double weapons = fast win, you can do the first 4 and half chapters (until before the Yeti boss fight) only with Dual HG.
- If you visited the secret dungeon Neverland (if you don't know what I am talking about don't even start NG+) assign Eagle and Hawk Eyes to your Dual HG wielder, it will save you some time (specially in Ch. 16, when you are forced to fight different times)
- RUN. You are probably at lv. 120+, you don't need to shot at every low level enemy you encounter; just sprint to the next area and you are done.
- In stages walk until the end of your turn (or until someone starts attacking to you - red icon near the nane of the character you are using), then -> Hero Action.
- You can end chapter 13 (Christmas presents) in no time using Hero Actions; use Lanne to end it even quickier.
- The achievement is unlocked after the credits, but you can skip them pressing Start