Rudra noticed that his dad was not actually dead. His body had somehow been sapped of all the natural mana it had , which led to him becoming shrivelled.
His blood was going cold very fast and Rudra had a feeling in his heart that the longer he took the more unlikely it would be for him to revive his father .
Rudra was not inside Omega and could not use solar restore at this moment to heal his father , and his arsenal was basically all attack moves except for that.
He desperately wished at this moment that he should have chosen the Hades special skill which allowed to bring back people from the dead at this moment , as now it would have been the best moment to use it , but with the lack of any options , Rudra decided to use darkness absorb on Nero , to try and steal his vitality to save his father.