One possible fanfic could be about Harry and Remus exploring a magical forest where they encounter a unicorn. The unicorn has a special connection to a magical animagus who can transform into a chair. Maybe the animagus in chair form holds a key to a hidden mystery in the forest that Harry and Remus need to solve to protect the unicorn and the forest's magic.
In a fanfic, Harry discovers that Remus has an unexpected connection to a magical animagus who can turn into a chair. This chair - animagus has a past with a unicorn. The story could revolve around how they all come together. Harry might be initially confused but as he delves deeper, he realizes it's all part of a bigger magical plan to safeguard an ancient magic related to the unicorn.
A fanfic could start with Remus telling Harry about a legend of a magical animagus that can transform into a chair. They then stumble upon a unicorn in distress. As they try to help the unicorn, they find out that the chair - animagus is the key to its well - being. The three of them - Harry, Remus and the chair - animagus - must work together to heal the unicorn and restore the balance of magic in the area.
I'm not sure which specific fanfic you're referring to. There could be many fanfictions that involve Harry being an Animagus and having some sort of connection with a chair and a unicorn. You might want to check some popular fanfic websites like Archive of Our Own or FanFiction.net and search for relevant tags like 'Harry Potter', 'Animagus', 'Chair', 'Unicorn' to find it.
A fanfic might be centered around a prophecy that involves Harry, Remus, a magical animagus in chair form and a unicorn. The prophecy states that only when these four elements come together can a great evil be defeated. Harry and Remus start searching for the animagus - chair and the unicorn. Once they find them, they have to learn to trust each other and combine their powers. The unicorn's pure magic, the animagus - chair's unique abilities, Harry's courage and Remus' wisdom will be the keys to victory against the looming evil.
A possible fanfic could be about Harry and Remus in a magical forest. They find a chair made of unicorn horns (not in a cruel way, perhaps it was a gift from the unicorns). A wolf approaches them, but it turns out to be a friendly werewolf under Remus' influence. Harry and Remus have a deep conversation while sitting on the chair, and the unicorn comes to join them, symbolizing the unity of different magical beings in their world.
I haven't come across such a specific fanfic myself. You could try asking in Harry Potter fanfic communities on social media platforms like Reddit. There are subreddits dedicated to Harry Potter fanfiction where fans are really helpful in finding or even creating fanfics with specific elements.
The plot could center around a magical chair. Harry and Remus find this chair in an old, abandoned castle. The chair has the power to call upon a unicorn and a wolf. When they sit on it, they are transported to a different dimension where the unicorn and the wolf are the rulers. Harry and Remus have to navigate this new world, understand the laws and culture there which are based on the relationship between the unicorn and the wolf, and find a way to get back to their own world.
Perhaps a story about an adult wizard who was cursed and turned into a unicorn animagus against his will. He then has to navigate the wizarding world in this new form, facing prejudice from some who don't understand his condition. Along the way, he meets Harry Potter and his friends, who help him find a way to break the curse.
One possible fanfic could be where Harry discovers he is an Animagus early on. His familiar could be a phoenix, for example. In this fanfic, the phoenix could guide Harry through difficult times, and their bond could be a source of strength against Voldemort. Harry could use his Animagus form, perhaps that of a stag like his father, to move around secretly and the phoenix familiar could provide additional protection and wisdom.
Back to the Future 1999 The Magical Unicorn's answer to the riddle is Quiet Ravenhart. If the answer is correct, the player will receive 20 pure raindrops as a reward. Pure raindrops were the tokens in the game that could be used to draw cards for free. Players could obtain the Magical Unicorn by completing missions or purchasing it. It had powerful magical abilities and could release powerful magical attacks and provide additional attribute bonuses to players, such as increasing attack power and defense.
Minerva McGonagall is also a favorite. Her Animagus form of a cat gives a lot of room for creativity. Fanfictions might show her observing Hogwarts in her cat form, seeing things that she wouldn't as a human, and using that knowledge to protect the school and its students.