Halter is a generally friendly person who is seldom angered. He is very loyal to Marie.
Vainney is a hulking man who is over two metres tall. He has brown eyes and buzz-cut grey hair.
He wears a red collar shirt underneath a business suit. He also wears a pair of black gloves and sunglasses.
Vainney is an 8th generation mechanized human. This makes his strength far beyond that of any ordinary human.
He can destroy some guard automata relatively easily.
Halter is first seen arriving at Kyoto with Marie's team in order to fix the malfunction in Kyoto's Core Tower, but Marie suspects something is not right since the Army hasn't interfered with their work.
After interrogating Ryouji Niijima, they learn that Kyoto will be purged. When the team hears this, they feel despaired, but they're encouraged by Marie.
After hours of work, they're still unable to locate the malfunction, and the Meister Guild are ordered to retreat by the government. Marie gets annoyed by this, and so she and Halter confront Limons Vacheron about the order. However, Limons is completely certain on purging the Kyoto grid, and strips Marie of her authority as a meister, making her unable to enter the Core Tower without permission.
After leaving his office, Marie and Halter, while thinking of a way to get back into the core tower, coincidentally cross paths with RyuZU and Naoto Miura. Marie almost immediately recognises RyuZU as the Initial-Y Series Unit that had been accidentally lost while being transported.
Marie attempts to negotiate with Naoto to return RyuZU to her, as she is the apparent owner of the automata. Naoto immediately refuses in a childish manner, annoying Marie. When she begins to threaten Naoto to return RyuZU to her, she doesn't realise RyuZU's scythes making their way towards her, intending to kill her. Halter is the only one who notices, and instinctively points his gun at Naoto.
After analysing the situation carefully, Halter realises that he and Marie are the ones at a disadvantage, so he tries to calm the atmosphere by putting his gun down and apologising for Marie's behaviour. She then begins to try and convince Naoto to help them fix the Core Tower, knowing that his hearing abilities would be able to detect the among the millions of gears in the tower, but Naoto once again turns them down, much to their dismay. However, when RyuZU informs Naoto that her "little sister" AnchoR - another Initial-Y Series Unit - is located in Kyoto's Core Tower, he then decides to go to the Core Tower to look for her, with helping the Meister Guild as a side-quest.
They soon rush to Core Tower in order to fix it before the purge begins, but Limons is insistent on purging the Kyoto Grid, and sends numerous automata to attack them. However, those automata are easily destroyed by RyuZU and Halter. In the midst of confusion, Halter and Marie agree to trick Limons into believing that she was killed, and smashes Marie's Chrono Compass, shattering it into pieces.
Halter is Marie's bodyguard. He is loyal to her and cares for her. He and Marie share a very deep bond and he has stated before that he will give his life for her as he is her bodyguard.
Halter and Naoto are shown to get along very well. He considers Naoto to also be a genius, much like Marie. He knows what to say in order to get Naoto motivated to do anything.
Vainny to Marie : You're still a child princess, the thing about being a child is you're allowed to cry. Nobody will judge you for it. - Episode 6
Vainny to Marie & Naoto : Pretty sure, that asking a kid if they like mom or dad more, is textbook example of bad parenting. - Episode 12