>Make that a character can rebirth for 10 times
>rewards : each rebirth gives +1 all stat so perhaps we can get +9 or +10 all stat bonus in the end (or you can suggest how much bonus stat)
>Challenge : second rebirth requires exp twice amount of first rebirth
the third is either 3 times of the first or maybe twice of the second rebirth
or maybe you have to complete a certain quest from the Valkyrie herself
>possible rewards : The Valkyrie fell in love with you and decide to marry you
or maybe some gears or a secret dungeon