WARNING! This will include spoilers with evidence through the whole series. Edit
This also includes opinions... EditPlease do not fight over who is better just simply state what you think and be done with it. Please do not ask each other if anyone really thinks that one ship or another will actually happen! Please and thank you!
Sophitz or Fitzphie is what Sophie and Fitz are called as a team by Keefe. They are extremely close friends and Sophie has had a crush on Fitz through the whole series. Fitz is the first elf Sophie had met and he's the one who showed her where she really belonged. He is also the only person who Sophie thought of when she was kidnapped, and she was capable of reaching out to him even with a phenomenal distance.
There was only one time when they didn't like each other and that was in Exile when Alden's (Fitz's dad) mind became broken. Fitz was really angry at her and said it was all her fault. He was so depressed on the inside that he just shoved it in Sophie's face.He later forgives her and apologizes multiple times for his acts. Fitz is the one with the closest relationship with Sophie because they are cognates-in-training with multiple trust exercises which includes telling all of their secrets to each other, then, later on, they become cognates which involves staring into each other's eyes a LOT. Along with Mr.Forkle, he is the only one capable of going past her mental barriers, and they trust each other very deeply. They get closer in Everblaze, and Fitz seemingly starts to show feelings for her in Neverseen, where Sophie comforts him upon learning Alvar's betrayal. He is also very excited that they are to train as cognates. Fitz really started showing his possible feelings for Sophie in Lodestar when he holds hands with her often, comforts her and is very protective of her. Sophie always has fluttery feelings or blushes around him. Under the Panakes tree, in Lodestar, we have reason to believe that Fitz tried to kiss Sophie when he told her, "Skip the talking" although they are interrupted by Keefe. In Nightfall, he prepares a lot of sweet treats and presents for her, and Sophie comforts him when they go see Alvar.
Fitz makes it clear that he is there for Sophie whenever she needs it and they support each other through difficult times (like when Keefe joins the Neverseen).
Keefe sacrifices everything for Sophie, having what he thinks is her best interests at heart, even though they sometimes are not. He is quite obvious about his crush on her, and straight out admits it in the Barnes and Noble Special Edition of Nightfall.
Keefe is always the first one to volunteer for anything that involves Sophie including a time in Neverseen when Dex makes a breathing-underwater contraption for two. In this scene, he wants to share it with Sophie (if they had shared, their faces would be extremely close together, their noses touching). Keefe also insists on being by Sophie and sometimes says things that also may seem flirtatious. He always says out loud in school multiple times, "It's a date, Foster!" sarcastically, but to show off when he comes over. He also tries to make her more relaxed and calm throughout all the books. Sophie never says she likes him but sometimes she gets the weird heart fluttery thing (ex: NEVERSEEN, Keefe and Sophie are by the mountains in the Sanctuary when it says, "...her stomach filled with fluttering things, which flitted around, even more, when she noticed how close they were now standing. The toes of their boots were almost touching, and his breath felt warm on her cheeks.") and shows that she cares deeply for him.
The two hold hands a lot, especially in NEVERSEEN, when Sophie seems to be the only one of the cast of characters really helping Keefe get through his hard times in that book. Keefe has also called her "cute" multiple times. During LODESTAR, both are there for each other during tough times: The Neverseen, Bad Memories, Mr. Forkle's death, and finding Sophie's missing family. In NIGHTFALL, they hug a lot, spend a lot of time alone together, and Keefe often has his hand around her waist. He paints her special painting with him and Sophie in the middle. In the extra scene, when Elwin gives him a sleep sedative he dreams about a pair of golden flecked eyes and is teased by Ro about how much he likes his "little girlfriend" (as dubbed by Ro) and he decides he will be whatever she needs, “until she was ready for more.”
Dexphie is a mix of Dex and Sophie and can possibly be a love match. Dex and Sophie have been best friends through the whole series and have a close relationship. Dex has always made cool contraptions for Sophie to keep her safe including the Sucker Punch (gives a burst of air so then your arm goes at a faster speed punching harder.) and a panic switch (a ring with a switch that will alert Dex to come help.). Dex was the "lucky" person and was going to see Sophie in the caves when the Neverseen came and kidnapped both of them doing horrible things like drugging and burning them. Dex always blushes with Sophie and takes any moments he can to be with her. He is always jealous with Fitz and how they always are with each other. In NIGHTFALL it's obvious Dex likes Sophie, but when he gets her some "Crush cuffs" as a cover-up to hide her Enhancing ability, Sophie kisses him. They both feel that there was no spark to the kiss, and they agree to be just friends. Dex then asks for some time to heal from her rejection, which she gives him. They are adoptive cousins, not by blood but by Sophie's adoption by the Ruewen's.
Tiana is formed by Tam Song and Biana Vacker,
In the book Lodestar, Tam "stole a quick glance" at Biana, which was possibly the start of his crush on her. It is noted that he admires her powers and bravery several times during the books. In Lodestar, Linh mentions that he likes brunettes, and Biana is the only brunette in their group. Also in Lodestar, Tam is mentioned several times in relation to Biana, including when Keefe makes clear that he is the president of the Foster Fan Club and Tam says he has no problem with that and looks at Biana, blushing.
Keefiana is the ship with Keefe and Biana. In the first book, Biana is jealous when Keefe calls Sophie for his base quest team. In Everblaze when Lady Gisela points a melder to Biana's head, Biana acts brave, though Lady Gisela claims it was "mock-bravery" to impress Keefe. In Neverseen, Keefe reveals he kissed Biana on a dare and Biana turned her head at the last second, and Biana is holding Keefe's arm on the cover of Neverseen. In Nightfall Keefe says that he flirts with everyone except Biana, just to make it obvious.
Winh or Lylie is the ship between Linh Song and Wylie Endal. After Wylie was taken and tortured by the Neverseen, Linh was always there to comfort him. He also becomes more alert during his treatment when Linh works with water around him.
Sizel or Grandor is the ship with Sandor and Grizel. Grizel has always been romantically inclined towards Sandor, and in Lodestar Sandor was there to comfort Grizel. Grizel constantly flirts with Sandor no matter if it could cost her her charge. In Lodestar and Nightfall, Sandor grows closer to Grizel, and they always have teasing moments.