Gareth Nightman

Gareth is the first teacher Sam and Taurtis meets who kills himself and comes back as a ghost.

Appearance
Gareth has brown hair parted to the left, with plain, light blue eyes. He wears the student uniform, a beige jacket with a white-button up shirt and a red tie, despite being a teacher. He also wears black jeans and black and blue tennis shoes.

As his depression gets worse, his state of dress also worsens. It starts getting torn and messy, and his face gets paler.

Personality
Gareth appears to be a gloomy person, as he is depressed once his wife, Jane, left him. Despite this, he also shows a caring side for his students, as he comforted Sam once after he was laughed at and gave him money.

He appears to be a bit of a push-over in Yandere, with Dom bullying him, pushing him to the ground or not letting him cross the street. He is willing to give Dom extra class privileges to leave him alone.

Gareth is a loving, and sad individual as we see throughout the series, with him loving Jane deeply despite her cheating on him. We also get the impression that he is incredibly lonely without his wife, as he seems to obsess over her and not do much else.

In his suicide letter, he still gives his class homework and expresses that he loved his wife very deeply and that he did not kill her. As a ghost, he haunts his old house and the school, asking people who killed his wife.

Rowan
Rowan and Gareth seem to have a close friendship, as they are implied to have regular movie nights. Rowan had a clear attachment towards Gareth, as once he found Gareth's corpse, he built him a grave at the back of the school and plants him flowers in his remembrance. Rowan was deeply disturbed when Paul Blart made an insensitive joke about Gareth's death, leaving the theatre shaking his head after seemingly having a fun time before. After Sam and Taurtis learn that the grave is Gareth's, they start to talk ill of him as they haven't had many fond memories with him, to which Rowan hits them both and says "I will break your legs", implying the deep bond between the two. It is also likely that Rowan was the only person alive that cared about Gareth, as there is no mention of an other grave, and Rowan built the grave for Gareth.

Jane
Jane is Gareth's wife, and they seem to have a deeply strained relationship. Gareth has expressed a deep love for Jane, while in Yandere the audience learns that Jane pretends to be a nice person to Gareth to keep his money. Jane actively berates Gareth behind his back, claiming that he is boring, and it is heavily implied that she cheated on Gareth with a frog, and she gave birth to Pepe. It is likely that Gareth knows this as he sings a song about how he knows that Jane is lying to him. Despite all of this, Gareth remains hopelessly devoted to her. At the start of Yandere High School, Jane has left Gareth leaving him in a depression. Soon after, Jane is murdered and Gareth is accused, causing him to commit suicide.

Taurtis
Taurtis seems to be the only person that Gareth actively dislikes. After Taurtis makes a comment about Jane, asking if she was single now, Gareth is deeply insulted and continues to stalk Taurtis afterwards. There is a scene where the ghost of Salex explains how she always loved him, to which Gareth adds that he didn't, insinuating that Gareth truly didn't like Taurtis. Once Gareth is a ghost, he continues to harrass Taurtis and accuses him of killing his wife. Once it is revealed that Yuki was the murderer all along, Gareth seems to finally forgive Taurtis and gets rid of his grudge.

Pepe
In Yandere, it is revealed that Pepe is Gareth and Jane's son, despite him being a frog. It is implied that Jane cheated on Gareth with a frog, and thus Pepe was born. Gareth is suggested to know this, but despite everything Gareth considers Pepe his son. It is unknown whether or not Gareth is resentful towards Pepe for what he stands for. However, Gareth possesses Pepe after Pepe moves into his old house, asking for answers about his wife. This event left Pepe in physical trauma, with him being a pale green.

Dom
Dom is shown bullying Gareth in the beginning of Yandere, actively harrassing him. Gareth claims that he will give Dom classroom privileges to leave him alone, but Dom refuses. That is about as much interaction they've had, as Dom joins Yandere High School after Gareth's death.

Trivia

 * Gareth is featured in the parody of "Super Smash Bros" in his ghost form in Tokyo Soul
 * Gareth's noose is left in his classroom, and it is claimed that it can never be taken down
 * Gareth's classroom was Room 23
 * The worse Gareth's mental health was, the worse his appearance was
 * Gareth had a noose on his wall before he committed suicide
 * Gareth's actor once tweeted out that after the finale, Gareth went to Disney Land for a few weeks where he met Mickey Mouse. Good for him, it's what he deserves
 * There is a fancomic and Tapas by WubzScribbles about Gareth's life in college in the 90s (self promotion squad)