Sorry - Mikasa x Eren x OC

Before you read this, I don't ship Eremika. It's just a one-shot. And plus, don't be offended if Eren x OC is my OTP.
And also, this contains spoilers from the manga. And also, this is an AU which Mikasa doesn't know of Saoirse's (OC) crush on Eren and their romantic interactions.  No hates please.

It was an ordinary day in the cottage where the new Special Operations Squad lived: Eren, Mikasa, Saoirse, Armin, Jean, Janessa, Krista aka Historia Reiss, Sasha, Connie, Rosemary and Levi. Since the original died, the corporal decided to recruit the recurring members of the 104th Trainee Squad. But for an ordinary day like this, this was Mikasa's special day.

"How's Historia doing?" Saoirse asked her friend Connie as they were assigned to carry boxes inside the cottage. 

"Well the current news we have of her is that she's donating money to the poor with Armin calculating the results," Connie told her. "Well, that makes her a real goddess."

Saoirse chuckled. "Well since she's a queen, she does act like one though she's serious already," she said.

The two already reached the area on where they need to place the boxes. As they were done with business, the two went to go separate ways. Connie is going to chat with Sasha while Saoirse decided to chat with her best friend Mikasa. Of course, they've been best friends since they met after she got rescued from the kidnappers.

Saoirse knew she was gonna be in the girls' room as always, so she made her way when she heard her friend's voice when she passed by the window that lead to the room. She dove under to not be seen and only peeked her head and eyes. She saw Mikasa, who was talking by herself.

Although it wasn't clear, she could hear it.

"Eren....I just wanted to say...that I loved you for years, and I don't know if Saoirse likes you...I hope you accept it."

Saoirse's body went numb after hearing it, and slumped against the wall. Mikasa had liked Eren? No way. Mikasa was her best friend, but there was no way she had to confess to him. She had to stop her, in a peaceful way.

She glanced back at the window again and saw Mikasa walk out. Taking this opportunity, she quickly ran around the cottage and into the entrance where she saw Mikasa walk to. When Saoirse entered, she realized Mikasa was gone. So she decided to search around until she heard voices.

She didn't seem to be anywhere in sight. As soon as she was about to go check the last room, she heard voices.

"Mikasa..?" she heard Eren say.

"Eren...I want to tell you something,"

Saoirse silently gasped. She's too late. But she had to do it fast before it truly was. She stood up and about to enter when the words she would ever hate for life was heard.

"Eren, even if you yell at me or think of me as a sister, it's more than that," Mikasa confessed. "I...I love you. Ever since you rescued me. You have taught me how to live, and I will be grateful."

She grabbed Eren's hands and looked at him in the eyes, blushing. "That's...that's why I'm protecting you...because we'll be together, right?" she said.

Eren began blushing, much to Saoirse's horror. "R..Really?"

Saoirse's gasp caught their attention, because they both faced her. Saoirse was so pale, she looked like a ghost, and she had pure horror and heartbreak on her face. The love of her life was taken away by her best friend. Betrayal. Suffering. Heartache.

"Saoirse..." Mikasa said nervously.

"I-I..." Eren tried to explain.

Before anything else, Saoirse ran away with a heavy stream of tears. Eren and Mikasa stared in horror, realizing the person they cared about was betrayed by none other than them. They felt so much regret, Mikasa was starting to regret her crush on Eren.

Saoirse's hands were clasped to her face, she didn't see who was passing by. She didn't know she passed by Rosemary, Janessa and Sasha who were chatting. As they saw the girl pass by crying intensely, they tried to reach her.

"Saoirse! What's wrong?!" Rosemary's sweet and caring voice called out.

"Are you okay?!" Janessa asked, concerned.

"What the hell happened?!" Sasha asked.

But the brunette ignored them, and continued to run away, even she ran out of the cottage and into the woods, showing she was so hurt, it was painful like being stabbed repeatedly.

Mikasa and Eren ran after her, only to be stopped by her friends.

"Guys, what happened?" Janessa asked.

"Saoirse...we're not..!" Eren tried to explain. "I've gotta follow her!" 

He ran after her. All three girls glared at Mikasa.

"We told you not to confess," Sasha said. "You should have seen her; she's so painful, she looked like she was stabbed millions of times!"

Janessa shook her head. "That's low, even for you," she said.

"How..how could you do that to your best friend? She trusted you! And would you steal what she loves?" Rosemary asked, voice cracking.

"I-I'm sorry..I never knew Saoirse liked Eren..." Mikasa's voice trailed off in sadness, about to cry.

"Well you should know," Janessa spat. "Best friends should stay true to each other."

"What the hell's going on here, brats?" the voice of Levi interrupted the scene, seeing the tiny figure walk in.

All girls looked at him.

"Corporal..." Rosemary said.

"And why did I see Hillman running away? What, the hell, did you do," he said.

Janessa pointed at Mikasa. "Saoirse likes Eren but she stole him away from her!" she explained.

"Sir...I-I never meant to.."

Levi glared at her. "Cleaning duty for two months." he said, walking away.

Rosemary, Sasha and Janessa gave dirty looks at her before walking away. Mikasa stood there, crying, and ashamed of hurting Saoirse, her own best friend, and disappointing everyone who cared about her friend.

Meanwhile, Eren continued to run after her. "Dammit! Where did she go?!" he said.

Jean happened to pass by him. "Nice going Yeager," he spat out.

"Shut up horse-face," Eren answered back, and continued to run after her.

For minutes, he kept looking for a brown haired girl in the forest before the cottage, but he never seemed to find her. He decided to go to a cave which was not far from the cottage. He reached it, and he looked inside. Nothing. Just before he could leave, he heard sobs.

He followed it carefully, and he reached a boulder. He looked behind, and saw Saoirse hugging her knees, crying hard. He walked behind and knelt beside her.

"Saoirse..." Eren said.

The girl raised her head up and glared at him. Her face was red and her eyes were puffy. "What do you want?" she asked angrily.

"Look, I know you think it's what it looks like but..."

"Mikasa's better with you, that's what it looks like," Saoirse answered angrily and buried her head into her knees.

"Why...why'd you and Mikasa betray me....you're...you're just her stepbrother...." Saoirse sobbed.

"I-I'm so sorry Saoirse," Eren apologized. 

"You don't look sorry if you like her but you came her for me," Saoirse replied.

"No, I came here because I love you," Eren said.

Saoirse raised her head up and stared at him. "What?"

"Like Mikasa said, I saved her from the kidnappers, but I only love her as a sister, I promise, because my heart belongs to you," Eren said. "I really like you, alot."

He grabbed Saoirse's hands. "Ever since we met, and I figured that I would never do anything to hurt you, nor Mikasa, she just cares about me like I'm her real brother. I mean it."

"Eren...I...I..." Saoirse choked.

Eren wrapped his arms around her back and pulled her into his chest. "Don't cry...please don't cry...I'm sad seeing you like this...but the two of us will be together, right?"

"I..I love you too," Saoirse said.

The two raised their heads and kissed each other. After that, they decided to go back to the cottage. As Eren was walking with Saoirse to the room, Mikasa came out and stepped in front of them.

"Mikasa...?" Saoirse asked.

"I'm sorry," she apologized. "Saoirse, you're my best friend, and I will never do anything to hurt you. But this is the biggest mistake I've ever done."

She grabbed Eren's hands and placed them on Saoirse's. "You...belong to her," she said. "You're my last family, and I love you, as a brother."

Eren smiled. "And I...love you, as a sister."

"Mikasa, thank you." Saoirse said.

She smiled. "I'm relieved to see you two together."

They heard giggles and saw Janessa, Rosemary and Sasha behind them.

"We just got here," the redhead denied.

"We didn't see anything!" Rosemary said, shaking her hands.

All of the cadets laughed.

*Bonus Ending*

"Hey Janessa, Rosemary?" Saoirse asked her friends.

"Hm?" they both said.

"Since Eren and I are a thing now..." she said.

"What?" Rosemary asked.

"Tell us," Janessa said.

"It's probably your turn to confess to Jean and Levi, that is, if another girl doesn't steal them away," Saoirse said, smirking.

Both of the girls turned beet red. "What?!"

"Come on! It's not like Sasha or Historia would steal them away, right?" Saoirse said.

Janessa and Rosemary threw their pillows at their friend.