Green Ranger Curse

One thing that Kuroninja is known for is how he and Lupin Yellow have been together since January. He has also formed relationships with at least 4 others. However, for some reason, Kuroninja always struggles to win over any of the female green rangers. This has led to what he calls the "Green Ranger Curse."

The Green Ranger Curse is the one reason why Kuroninja has trouble forming relationships with female green rangers.

Possible Causes
The Green Ranger Curse is probably just a coincidence. However, Anti-Kuroninja is associated with the color green because of his group, known as Emerald Club. Since Anti-Kuroninja's group is mostly green rangers, including himself, it might've affected Kuroninja's luck with green rangers.

Another reason why Kuroninja has bad luck with female green rangers is probably because he doesn't get along with some green rangers, such as Patren 2gou, DragonRanger, and Flower Ninja Suiren. It might've formed into negative green ranger karma for Kuroninja.

MidoNinger
Luna Kokonoe used to be the apprentice of Kuroninja, but then when she joined the Ninnin Girls, she got possessed by the spirit of Kyuemon Izayoi and then she stopped being Kuroninja's apprentice.

Chameleon Green
Kuroninja wanted to start a relationship with Hammie but then the Battle of the Kyuranger Fanfictions happened and she ended up with Naga/Hebitsukai Silver at the end.

Kiramai Green
When Kuroninja and Sena Hayami first met, Anti-Kuroninja appeared and invited Sena to join Emerald Club, using the Green Ranger Curse to his advantage. Kuroninja then got attacked by HurricaneDark before he could go on his first date with Sena, which convinced her to join Emerald Club.

For some reason, Kiramai Green is still in a relationship with Kuroninja despite being a green ranger, and she is part of the Core 7. Kiramai Green could be the one to break the Green Ranger Curse.