Milleth looked at Reif with a pitiful and desperate look on her face. She was desperately trying to cling to her only hope remaining that is not actually her hope
She sees Reif as a naive and innocent kid that is easy to deceive. Milleth thought that Reif will pity her and she'll stop Rhash from killing her
However, there is one thing that she doesn't know and that is Rhash's importance to Reif
Even if Rhash were to say that fire is cold or he was ordered by Reif to do the most dangerous thing in the world, this naive and innocent kid would still believe and obey Rhash
To Reif, Rhash's order was even more powerful than an Imperial Edict
Seeing how unstable his big brother's mood was, Reif decided to obey him as soon as possible
Maybe, when Milleth died, Rhash would finally calm down. Thus, without hesitation, Reif sent a beam of energy straight to Milleth's head, poking a gruesome and gaping hole in it