Adrigaminette

Adrigaminette is the polyship ship between Adrien Agreste, Marinette Dupain-Cheng and Kagami Tsurugi from the Miraculous Ladybug fandom.

Canon
Because of Adrien kind words and gestors towards both Marinette and Kagami they began to develop romantic feelings for him, while he simply sees them as friends. Even though there have been time where Adrien has shown to deeply care about both girls. While Marinette and Kagami have on occasions see each other as rivals for Adrien's affections; that tension between the two girls later blossomed into a friendship in "Ikari Gozen". Where Kagami, as the dragon-themed superhero Ryuko, was given the chance to fight beside Ladybug and Cat Noir and later became included in their trademark pound it. All while being unaware that they are in fact Marinette and Adrien, even though the two know that Kagami is Ryuko.

Season 2
Riposte
 * The three met each other at the academy's fencing tryouts.
 * Marinette watches Adrien trying to talk with Kagami from the academy's steps, before Kagami got into her car.
 * Marinette watches Adrien and Kagami talk to each other, again, while standing behind a billboard-like stand.
 * Kagami is seen "standing" between both Marinette and Adrien, who both might have been looking back at Kagami, in the end card.

Frozer
 * The three are seen in the end card, where Marinette is seen as her civilian and superheroine self.

Season 3
Animaestro
 * Marinette is seen looking at Adrien and Kagami, in the end card.

Oni-Chan
 * Adrien is seen "standing" between both Ladybug and Kagami, in the end card.

Ikari Gozen
 * Kagami tells Marinette that she's understanding what Adrien has said about her.

Fanon
The ship could simply be due to Adrien being close with both dark haired girls, of east Asian descent, who have their own romantic feelings for him, while his feelings for Ladybug has him viewing the two as friends. Some have Adrigaminette rival with Lukadrinette (Luka, Adrien x Marinette), since they both serve as compromise ships.

The season three episode, "Timetagger", reveals that during the time of their adulthood, Ladybug and Cat Noir have assembled a team of Miraculous holders, that might have Kagami as one of its members. As well as the fact that they'll be facing a different holder of the Butterfly Miraculous who might not know that Ryuko is Kagami, in which might make it safe for Kagami to be entrusted with the Dragon Miraculous again, without putting her family and loved ones in danger.

On AO3, the poly ships has only 4 fanfics about it.

Fandom
FAN FICTION
 * Marinette/Adrien/Kagami on FanFiction.Net
 * Marinette/Adrien/Kagami on FanFiction.Net

TUMBLR

Trivia

 * According to Feri González, Kagami isn't limited to the role of alternate love interest, the same with Luka Couffaine.

Variations

 * Adrienette refers to the ship between Adrien and Marinette
 * Adrigami refers to the ship between Adrien and Kagami
 * Kagaminette refers to the ship between Kagami and Marinette