Back again after update, This story blooming rather beautifully, not sure about the Chaos skill but I am starting to like Umbra skill, I almost defeated that pesky sister of MC, overall satisfied on how Umbra skill right now, I guess with little bit of training MC would turn out great.
Malefic skill is great as well but very mana heavy, I am previously defeating MC sister with this skill tree, just roll the dice at stun and poison her constantly, although defeating her will need some save exploitation, I believe Umbra is capable defeating her as well if keep reloading the save.
Would try chaos skill next.