MenSaku

MenSaku is the het ship between Menma Uzumaki and Sakura Haruno from the Naruto fandom.

Road to Ninja: Naruto the Movie
At the bath house, Menma's name was mentioned by Hinata as she asks Sakura if she and Menma have any special relationship.

Sakura and Menma's first meeting happens when the latter goes back to Konoha to demand the scroll. He starts fighting with Minato, Kushina and Tsunade, and easily overpowers them, but instantly later, Naruto and Sakura arrive to the scene. When they realize he is the masked man that Tsunade mentioned earlier, Sakura tries to land a hit on him, but he slams her down to the ground. Menma takes this chance and kidnaps her.

Later, when Menma is possesed by Tobi and is extracting Kurama from Naruto, Sakura shows up and attempts to land a hit on him again. He easily avoids it and they start fighting until Naruto's memories return.

Road to Ninja CD Drama: Road to Charasuke
As the events start, Naruto and Sakura have been in the Limited Tsukuyomi world for one day. Alternate Hinata are going to Sakura’s house to warn her not get too close to Menma with alternate Ino follows her as she tries to convince her. When Hinata and Ino arrive, Hinata notices that Sakura seems very happy after she received a rose from alternate Sasuke.

When the girls ask Sakura about the rose, they were surprise when Sakura says that she doesn't feel anything for Menma. Ino then tells Sakura that it can't be right because with Menma, she [Sakura]... but Ino is quickly cut off by Hinata who says that Sakura's change of heart is completely welcome and she will support her.

Naruto Shippuden
After Madara awaken the Infinite Tsukuyomi, it sends everyone (excluding Naruto, Sasuke, Sakura, Kakashi, and the reanimated first four Hokage) into a comatose state where they dream. In Tenten's dream, she is taken to the setting of Road to Ninja. There is revealed that rather than being in love with Sasuke, Sakura has feelings for Menma and is rivals with Hinata for his love. However, Menma is not interested in either of them and calls them a pain. Sakura blushes in Menma's presence and always stands by his side in every scene.

Fanon
MenSaku is a fairly popular ship in the fandom as it is the alternative version to NaruSaku, it gained many fans in Road to Ninja and still has it's fans.

It is a common trope with this couple that Menma has turned "evil" and that Sakura is the only one that can save him, Menma is mostly written more explicit that Naruto - often swearing, talking back and fighting more and sexual towards Sakura.

Fandom
Menma Uzumaki/Sakura Haruno on Archive of Our Own

MenSaku on Tumblr

Trivia

 * Minato realizes that Naruto wasn't in a good mood and asks him if he had an argument with Sakura. This suggests that maybe Menma and alternate Sakura had a close relationship and that both Minato and Kushina were aware about that.
 * Kushina teases Naruto about wanting to "look good" in front of Sakura. This may imply that Menma also had feelings for Sakura in the Limited Tsukuyomi World.
 * When Sakura says that she does not have feelings for Menma, alternate Ino and alternate Hinata were surprised that Sakura suddenly changed her heart. This could be mean that alternate Sakura has feelings for Menma.
 * Alternate Ino is trying to say something to Sakura about her when she is with Menma. This could be indicate that alternate Sakura feels happy when she is with Menma.
 * Alternate Sakura has strong feelings for Menma and constantly fights with Hinata for his affection.
 * In almost every scene containing Menma, Sakura is next to him and occasionally blushes at him.