I’m recently starting to play Call of Cthulhu 7e, and really enjoying it. My Investigator is also enjoying it so yay, this Keeper is happy. However, we just finished our first Scenario and she asked me a question I cannot seem to answer:
How do you increase HP Max to survive more fights? Is it simply increasing your CON or SIZ? I am pretty sure the rules say you can only increase skills, not characteristics, right?
Best Answer
You don't.
Simply because you're not supposed to survive more fights, CoC is about a desperate struggle with overwhelming odds, that will end in doom, not about some epic tale where nobodies defy their fate to save the world.
Technically, the only way to increase HPs would be to increase stats and you've apparently read the answers to the other question so you know it's pretty much impossible.
You could of course design magic items or spells to increase HPs, but this is what mad sorcerers do and they never end up as investigators (meaning, dabbling with magic in CoC will drive your character mad at an even faster rate than the regular mysteries).
Nevertheless, if you think you'd enjoy a pulpier version of CoC where blasting monsters is actually a viable option, there is a slightly modified version (appropriately called "Pulp Cthulhu"...) where, among other things to beef up investigators, you get more HPs from the beginning (but still without a reliable way to increase them as character progression).