Shinirai

Shinirai is the Femslash ship between Hamato Miwa/Karai and Shinigami from the Teenage Mutant Ninja Turtles fandom.

Canon
Throughout the scenes featuring Karai and Shinigami, Shinigami is seen to be tenderly touching Karai's shoulder and comforting her. She is clearly very close to Karai and trusts her judgement.

In Season 4, episode 15, City at War, Karai introduces Shinigami as a close friend from Japan to April and the turtles. Shinigami is also her second in command. Shinigami seems to trust Karai and has respect for her as she refers to Karai as Senpai and follows her lead. Shinigami is also shown to care deeply for Karai as she goes from blowing a raspberry at the turtles to looking at Karai sadly when Karai's shoulders slump.

In Season 4, Episode 16, Broken Foot, Shinigami and Karai are once again seen together and work together to take down one of Shredder's buildings. Despite being interested in the money, Shinigami still let's Karai do what she wants with it (in this case, burn it.)

Season 4, Episode 20, The Super Shredder, When Shredder comes to confront Karai, Shinigami fights with Karai to take down Shredder yelling at Shredder that she will take him down for all the things he's done to Karai. When Shredder has Shinigami knocked out, Karai willingly surrenders to keep Shinigami safe.

Season 4, Episode 25, Requiem, shows Shinigami pushing others out of her way so she can get to the unconscious Karai, she thanks Leo for saving Karai and eagerly agrees to keep watch over Karai while they wait for the ambulances.

Season 4, Episode 26, Owari, Shingami attends Splinter's funeral despite not having a close relationship with probably out of respect for Karai who could not make it.

Fanon
Shinirai became a popular ship after Shinigami's debut episode as it was a better alternative to Leorai (who are siblings). Though there isn't anything canonical in the show fans have pointed out that Shinigami is shown to be touching Karai quite tenderly and they seem to be very close even for friends.

The non-canon Ice Cream Kitty song video also featured Karai and Shinigami holding hands in what could be intrepid as a romantic gesture with a pink background.

Peter Di Cicco - one of the writers of TMNT 2012 has actively shown their support for the ship referring to them as ninja girlfriends in one tweet + in another, talking about how Shredder and Splinter would argue on who get's to walk Karai down the isle at her and Shinigami's wedding. Another tweet has him stating that Karai and Shinigami are his OTP

Fandom
Karai/Shinigami on Ao3

Karai & Shinigami on Ao3

Trivia
• Shinirai tends to be the rival ship to Leorai

• A good amount of Shinirai fans were Leorai fans before it was revealed that Karai was Splinter's daughter