She's the most serious-minded of the eight Valhallan princesses and stickler for the rules. She made a brief appearance in the first series, and plays a role in the third. She is considered the adjudicator of the Royal Family and has a special attack called the Thrust of Death, which sends anyone to the Punishment Dimension. Everyone fears her, even the violent Hydra. Inarba enforces the Law of Valhalla, and any offenders she meets will suffer the Punishment Dimension, which causes them to live out their greatest fears or some ironic punishment. Laine wasn't affected by it because she didn't pay any attention to what was going on when she was sent there. She comes to Earth to judge the members of the Royal Family and to make preparations for Kazuto and Valkyrie's wedding during the Stellar Season. So far, only Kazuto's sister was able to counter Inarba's Thrust of Death, in which the impressed Inarba declares Rika to be her eventual successor, though Rika sees the training as just more homework.

from wikipedia