Grui has long light-blue hair with bangs loosely tied on either side and a long braid across one side. He has heterochromatic eyes (colored red on the right and blue on the left). His attire consists of a dark red cheongsam paired with black tights and matching boots. He also has sharp piranha-like teeth.
Immediately upon the debut, Grui displays a haughty characteristic, first contemptuously chiding the 5th Elder and Kentas for not doing their work right and then ironically thanking them for providing the opportunity to hunt properly. He is quite talkative compared to his rather silent partner, Gaitan. He revels in wanton barbarity as he indulges himself in slaughter of humans, causing more devastation than needs to be.
Grui is introduced, as he appears with his partner Gaitan, to assist Lunark and Kentas in the mission to hunt Muzaka as per their Lord's order. They arrive when Lunark and Kentas have been complaining of the incredulity that their Lord decided to call upon those savage werewolves. Grui speaks up, answering Kentas that they are the ones at fault for not doing their jobs properly. He ironically thanks them as they can finally go for a real hunt. Heated exchange of words between Kentas and Grui follow. Grui informs Kenatas that they are not too happy about the whole situation either. He comments that he detests Kentas' warrior-like attitude and Lunark's human-like attitude after becoming accustomed to human world. Kentas laughs off his comment and asks him if that is how he ranks their Lord, as their Lord is an Elder of Union just like Lunark. Grui gets aggressive but Lunark steps in to stop the duo. Grui disapproves her authority, however, Lunark reminds him that she has been put in charge of this mission by their Lord. Grui still refuses to take orders from her and reminds her that she is not superior to them just because their Lord gave her the leadership. Lunark invites Grui to get wild as he pleases on the spot and as Grui starts to get really irritated, Gaitan stops him and reminds him that at the moment it is a priority to obey their Lord's command.
Throughout the briefing of their mission, Grui keeps pointing out that Muzaka 'was' the past leader and a traitor whenever Kentas speaks of him with reverence. Lunark draws conclusion by reminding the team that their task is to capture Muzaka and if that is impossible, to kill him. Grui likes the idea and laughs excitedly. Lunark gives further information and rules, telling them to remember not to conflict with the enemy nor be discovered by the Union. Gaitan reveals to Grui that there are not only Noble clan leaders but also their Lord which really intrigues Grui. Lunark instinctively instructs Grui to not act upon his wild thoughts but Grui shakes her instruction off and they take their leave.
After reaching the mission location, Grui and Gaitan take down the KSA agents who confronted them. Grui picks up a trace of a werewolf in the vicinity and concludes it can only be Muzaka. The two werewolves follow it without knowing that they are actually mislead by the traces Yuri had planted. As they approach the park area, Grui sets off devices to cause a blackout in the area as well as block all incoming-outgoing communication networks.
Grui and Gaitan are then lured by Rael who has decided on the action so that Regis could lead the children to safety. The two werewolves chase the young noble to an uninhabited island. However, Grui is disappointed at learning that there is no ambush of nobles waiting for them. He reveals he let the noble guide them just so that they could reach the hide-out of clan leaders. So, Grui decides to vent his anger on Rael and the fight begins. Rael's agility catches Grui's attention but his attacks are too futile. However, when Rael brings out his soul weapon, Grui, mistaking Rael for a clan leader, decides to get serious and transforms into a werewolf. The battle continues as a one-sided fight but just as Grui is about to land a direct hit on Rael, Regis intervenes. The dual attack results in a scar across Grui's face. Incensed, Grui then goes all-out to finish the nobles and avenge his humiliation. He easily throws off Regis and continues to beat up Rael. However, after Regis obtains the Landegre clan's soul weapon, the tables are turned on him and Grui is overpowered by the two young nobles. Before he is completely defeated, Gaitan steps in the battle to buy him enough time to heal.
Afterwards, the modified human trio (Tao, Takeo and M-21) enter the scenario and battle out with Gaitan while Grui stays along the sideline, healing himself. When his major injuries are healed, Grui takes his chance to land a surprise attack on Rael and Regis. He easily defeats the young nobles, who unlike the werewolf, are unable to heal so fast. Grui then aims his finishing blow at Rael. But Rai arrives just at the nick of time to save the young nobles.
Grui is irritated at the intervention of the stranger who he mistakes for a clan leader. He continues to provoke Rai to fight but is infuriated at the latter's nonchalance. He aims an attack which is easily deflected by Rai. Suddenly, another powerful presence catches their attention and it is revealed to be Muzaka.
After Muzaka convinces Rai to stop interfering with his 'family' issues, he turns to Grui and Gaitan. When Muzaka questions their inclusion in his family seeing that they have undergone modification, Grui retorts at 'the traitor' of the werewolf race who has decided to show up rather than hide. He praises their current Lord, Maduke and corrects Muzaka that they have come to kill, not just capture, him. Following this claim, both Grui and Gaitan launch a joint attack at Muzaka. However, Muzaka, who is incensed at the fact that Maduke has only sent two minions to kill him, transforms and easily takes out his opponents. Grui is sliced into halves by Muzaka's claws.
As a werewolf, he can use transformation ability to increase his powers and improve his bodily features. However, unlike many other werewolves, he possesses unique transformation. Following his eye colors, he has two distinct fur colors: red and blue. While his right side has red fur, his left has blue fur; his claws are also colored with the same colors. After transformation his physical and spiritual abilities are enhanced.
From the expression and conversation of both the 5th Elder and Kentas, it can be assumed that Grui is stronger than the aforementioned werewolves in terms of savagery. During his fight against Rael, Grui easily overwhelmed him. After his transformation, his strength is increased dramatically. He can use pinkish slashes from his claws which easily wounded the high-ranked Noble. Grui also possesses incredible speed, he can move and jump far ranges in mere seconds. His speed allows him to leave an afterimage and is equal or even superior with Rael's speed (who is from the clan known for speed). As a werewolf, he has high speed regeneration. He can heal his injuries, even fatal ones, in mere seconds.
Rare ability among the werewolves, Grui is able to manipulate his inner energy known as "aura" very proficiently. He has shown an unorthodox ability to track traces left by werewolves with the use of his left eye (the blue one) which runs a blue-colored laser scan off the field. However, he is unable to confirm the identity from trace (judging from how he relied on assuming that Muzaka can be the only werewolf other than them present in the vicinity). He is able to use very-fast white-colored energy beams from his palms and also use them as a slash. During the battle against Rael, he created a tornado from his pure aura by spinning at a high velocity. He can also use his claws as a medium for his aura attacks.