Charisma is very slow to upgrade compared to others stats.
If I remember, there is an event with the goblin girl at the bar where you will need at least 8 points to talk or something (message check status pass or something).
Just train the 4 stats to 10, it's quite easy :
- charisma : work at cow girl stall, work at the oni's place or work at the bar
- strength : work as a lumberjack where there is the orc
- dexterity : train at gnome's place
- inteligence : learn in library where there is the lamia
You can check your status and stats with your helper (green fairy).
Maybe you already maxed out your stats.