Grimsby is an attractive, young adult. He has his light-colored hair slicked back into a tidy hairdo with a small section worn as a long bang, which curls slightly at the end, over his left eye. One of his ears is pierced; he dons a long, dangling earring in the shape of a seahorse. Grimsby dresses in a neat tuxedo with a polka-dotted bow tie.
Grimsby is a somewhat dramatic, confident individual who is passionate about his job in the theater. He interrupts Ciel Phantomhive and Arthur Conan Doyle's conversation to discuss theater, and expresses an interest in working with Ciel in the entertainment industry. He considerably loves Irene Diaz, becoming enraged when Georg von Siemens continues to grope her despite her protests. He is very protective of her, as he had furiously disapproved with the Phantomhive household servants questioning her.
Grimsby is prone to outbursts, to the extent that Irene was often compelled to soothe him or hold him back. When angered, he is impulsive and belligerent, as he had tossed a wine bottle at Georg. He is sensitive and extremely averse to being accused of a crime; he frequently defends himself with stark vehemence, and is predisposed to pointing fingers at someone else.
Phantomhive Manor Murders Arc
Grimsby is invited to a party thrown by Ciel Phantomhive and mingles with Irene Diaz, his significant other, in particular. He and the other guests exchange greetings and commence introductions. Later, he interrupts Ciel and Arthur Conan Doyle's conversation, bitterly agreeing with Ciel's statement on the unfair fact that as long as one has authority, one would be enthusiastically praised even if one's writing may be rubbish. When he sees that Irene is distressed by Georg von Siemens's advances, he responds by throwing a bottle of wine at Georg's head, which Sebastian Michaelis intercepts and uses to fill wine glasses. This establishes tranquility among the guests, and they resume the revelry. When Grimsby catches sight of Irene looking at Sebastian, however, he scowls in displeasure.
In the midst of the festivities, Grimsby and the other guests hear a loud scream from Georg. They rush to his bedroom; inside, they discover, to their unanimous horror, that Georg has been killed. Grimsby suggests that they refrain from moving his corpse until the Scotland Yard arrives, but Baldroy sternly disagrees; he explains that the body will rot fast if they do not immediately transfer it to a cold, dark room. After the said body is moved to the cellar, Grimsby and the guests speculate on how the murder happened. Grimsby and Karl Woodley throw accusations at one another, and subsequently, each guest is obliged to state his or her alibi. Grimsby claims that he and Irene were in the Billiards room at the time of Georg's murder. They eventually narrow down the prime suspect to Ciel, and when one guest is asked to maintain a vigil over him, Grimsby states that he would not allow for Irene to be by herself. After they decide that Arthur will keep a watch over Ciel, Grimsby and the other guests are escorted to their respective rooms.
Later, Grimsby and the other guests discover the brutal murder of Sebastian. Grimsby exclaims his distaste for the manor, as two deaths have occurred overnight. They resolve to move Sebastian's body to the basement for the time being, and Grimsby and Irene follow Charles Grey to the dining hall. At the dining table, Grimsby asks Irene why she has not touched her food, and she replies that she is not very hungry. Grey offers to eat the plate next to hers, and that is when they collectively realize that it belongs to the mysteriously absent Patrick Phelps. They opt to check on Patrick, who was assigned to Ciel's bedroom. When they find that the door is locked, Grey swiftly cuts it down, to Grimsby's shock. They hurry inside, and discover Patrick's corpse. Grimsby wonders if they are in some kind of nightmare.
Later, they have dessert at the drawing room, where they discuss about the three murders. Patrick has a stab on his neck that resembles the penetration of a poisonous needle, and since Lau is carrying a needle, Grimsby and Karl rashly jump to the conclusion that Lau is the killer. Arthur shortly declares that there has to be more than one murderer in order for the string of murders to occur, and Grimsby explodes in fury, complaining that on top of being trapped in the manor by the storm he is treated as a criminal. Ultimately, they allow for Arthur to dictate their actions from here on out, as through deductive reasoning, he is the only one who could not have committed any of the crimes. Arthur asserts that they will be moving as a group wherever they go. They decide to investigate Sebastian's body, and Arthur says that since it is difficult to ask Irene, a woman, to accompany them to the corpse's storage room, he asks Grimsby to stay with her.
Subsequently, Arthur explains to all the guests that their rooms and belongings must be checked, and they give their consent. Later, they gather once again in the drawing room. Grimsby remarks that the silence is rather suffocating, and offers to get some cards from his room so that they may play, but Arthur says that it is safest if they all move and stay in groups. Lau, then, introduces the idea of a thirteenth person being among them.
Soon after, Jeremy Rathbone, the "thirteenth person," is brought to them, much to their astonishment. They try to verify that Jeremy is not involved in the murders. When Ciel asserts that he is not, with a letter previously written by Sebastian, Grimsby shouts that Jeremy cannot be proven innocent with just a piece of paper, especially since Jeremy came from the outside. However, in Jeremy's coat pocket is a ticket for an evening show of March 12th, which indicates that Jeremy has not committed the murder the prior night. Later, Jeremy leads the investigation.
For dinner, they eat a scrumptious steak meat the Phantomhive servants have prepared. Lau presses for the truth behind the incidents, but Jeremy tells them to not be hasty.
While Jeremy implements a plan to catch Patrick's killer, Grimsby and the rest of the group gather in Karl's room to wait. Tanaka appears at the door to announce that they were successful in capturing the killer, whom of which Jeremy reveals to be a snake. They reason that the snake must have been smuggled from Africa, which shifts the attention to Karl, who specializes in African trade. Jeremy asserts that alibis do not worth much, and Grimsby questions this. According to Jeremy, Georg was in cahoots with someone and had initially faked his death with a substance in an ampule he threw into the fire; however, Georg was actually killed later by the person who had killed Sebastian and retrieved the ampule from the fire. The said person, then, attempted to destroy the evidence, and Ciel suggests that it might be found in Karl's hearth. Grimsby demands for the evidence, and searches the hearth. They, then, discover glass shards, in which Jeremy reassembles to the ampule. Grimsby aggressively proclaims that Karl is the murderer, in spite of the latter's fierce denials.
Grey, then, shackles Karl and escorts him to jail. Grimsby and Irene voice their relief that the case is solved. When the Phantomhive servants point out that they have discovered a dark red liquid in Irene's room, Grimsby yells at them for questioning her. Jeremy clarifies that it contains an extract of red perilla which brings about an anti-aging effect. Embarrassed, Irene reveals that she wants to remain young with Grimsby forever. They, then, use some of the liquid to toast in celebration of the solving of the crime. As soon as the sky clears up, Grimsby leaves on a carriage with Irene.
- Sebastian Michaelis finds out later that Grimsby and Irene Diaz have separated, presumably due to heartbreak, as she is currently in a relationship with Julius Pitt.