Is there a way to rapidly too increase and i need to know where because the other candidates got 200 + hp in 2 days ( in easy mode )
There's a black market merchant that sells 2 cards that allow you to gain 100 height in a single match when both used. You can find that merchant at the arena inside at night time. That's the easy method. There are other cards cards that allow you to gain height within a match. It's up to you to find them.
The black market merchant also sells an HP booster which gives you max hp at the end of each day, but there are some brutal boss fights that will require you to gain way more hp than the booster can give reasonably quickly however. Thoroughly explore the casino in order to get the other hp source that isn't locked behind a boss fight that makes final boss Valeria look like a chump.