How can I increase the maximum HP for in-game achievements?

[danliz]

How can I increase the maximum HP for in-game achievements?

[Mr. September]

Mainly, exploration. The map is peppered with +5 HP crystals. You can also buy one of the +20 HP crystals, I think? Another might also be a quest reward.

[danliz]

What kind of quest?

[Scorpix]

You need to give red crystal (quest item) to robot who is standing on guard in the first hub area on the right.

[Mr. September]

You eventually get hold of Quest Items. Walking past the NPC who's interested starts a dialogue with them, so you don't really need to look for the exact NPC. Running from one end to the other of the hub usually lets you turn in stuff easily.

Some NPCs are in far places, of course, but they aren't hard to guess. The only one I didn't think of was the Black Perfume, and even that wasn't difficult.

[danliz]

Thanks guys, it turns out I did this quest and the last crystal was in the final boss' room.

[Alice Izuragi]

i collected everything, and my max hp is 470 and not 500.
including the hp increase item in the final boss room