Ponyville has always used to be a quiet town with friendly ponies and where anything exciting things can happen. But ever since Sweetheart came to the town, things has changed by time.
In fact the ponies was quite happy for her, even Twilight was happy for her ever since she decided to stay with Twilight, where she helps others with their daily schedules. For example, where Rose Luck had forgotten to deliver a bouquet to Matilda, who has a friend on visit, Sweetheart just showed up and volunteers herself to deliver the bouquet to the donkey lady. Everypony was so happy for her and showed their gratitude to her helpful spirit. Even Twilight felt joyful for Sweetheart to feel welcome in the town and finally has found a place that made her useful to both the town and Twilight as a newcoming princess.

One sunny day she saw Sweetheart, walking along with a pony that has a dark liliac cape with a hood which covers the entire head except for the muzzle. Twilight was not sure if it's a stallion or a mare, but this mysterious pony was very tall. Just as tall as Princess Celestia.
Twilight follows them with her eyes, and when they stops to the path that leads to Everfree Forest, they separated and the mysterious pony disappeared in the woods, while Sweetheart was on the way back to the town. She was heading to Twilight, who's quickly looking down and pretended to check the list of duties. Sweetheart asked her if there is something she can help with. Twilight responded with a yes and gave her a stack of lists.
"Sweetheart... Who is this mysterious pony, you were walking with?" Twilight asks curiously, while she gives Sweetheart some papers. Sweetheart paused for a moment, but she replied that the tall pony was just a traveller who´s just asking for directions. After Twilight has finished to give Sweetheart half of the list, she quickly explained to her what she´ll do in the lists. Sweetheart nodded understandable and went herself in the process of performing lists.
Twilight was happy to have somepony who can help her to fulfill the rest of few things she can´t mangage to finish. She's almost like a assistant (Spike is still her assistant #1, so that would make Sweetheart her 2nd assistent). While she was doing some obligations, she was wondering about Sweetheart and the mysterious pony who disappeared in the woods, like a shadow. It almost feels like they know each other...

One beautiful spring day, Twilight and the ponies organizes a midsummer festival in the town square. Twilight has never been a festival, but she has heard stories about how pretty the star-shaped decoration at the buildings and the lanterns floating elegantly in the sky.
She has heard that noble aristocrats celebrates it and took place in Canterlot ballroom or in the royale garden, which she never notices before, but today Princess Celetstia offered them to celebrate the festival for the first time, which makes everypony stamp by joy. Which makes Twilight to wonder how she´s never heard it before and how could it be that everypony knew about that? Even her friends was talking about it.
She was at a table in the city street and helps Rarity to cut some gold papers into stars and sometimes moons, and hangs them with the ribbon which was hanging on a bushy rod which was called a "Maypole"."

"Rarity... How come I've never heard about it when you knew it?" Twilight asked curiously.

"Well darling, I've never heard it either, but since I hears rumors about this 'magnificent' festival, I was obsessed with it and hopes we could celebrate it in Ponyville. And my dream came true!" Rarity responded and seems quite tense and honorable for helping to arrange it. Twilight smiled slightly at the thought of a dream that would come true. Her little daydream was quickly disrupted by Lyra Heartstrings, who asked after Sweetheart.

"Sorry, but I'll tell her when I see her," Twilight said just as she sees Lyra nod and walked away.

She thinks it's weird that Sweetheart just disappears when there are other ponies, who needs her help. "Don't you find it odd, when Sweetheart just disappears for a moment?" Twilight asked suspicious to Rarity, but Rarity replied simply that she´s probably has other plans to do.
Twilight didn´t say anything and continues to decorates in the town. But it´s strange that many ponies´s never wondering, where Sweetheart could be or what she was doing. She has a feeling that somethings is going on strangely. She and Rarity finished the decorations, Sweetheart appeared suddenly and her expression looks so ordinary happy. Twilight asked her where she had been (almost trilliard times the other days), but she got another excuse (and sometimes the same excuses) to have found some beautiful flowers for the party.
She shows them as evidence and Rarity were so admired by golden tulips which she has never seen before. Twilight wasn´t impressed by the flowers, but thinks they are pretty. Sweetheart gave them to put some flowers as decoration, but before Twilight could tell about Lyra, she said suddenly that she knew and have already given the strings of her harp and pointed the direction. Twilight followed the direction and to her surprise, she saw Lyra practices with her ready-made harp and waving to Sweetheart as she could hardly believe her eyes.
How did Sweetheart know that Lyra lacked some strings to her harp concert, when she has been gone for nearly 3 hours? Twilight was just about to ask her about it, but when she turned around, she was already gone. Rarity immediately said to Twilight that she would help Applejack while she adored and admired the tulips.
Everything seems pretty strange recently. It's almost like everypony (especially Rarity) didn´t thought about where she got the tulips from? It´s strange that others didn´t notice that Sweetheart goes into the woods every day and disappeared like magic. She has seen her go into the woods a lot of times and gives her the same excuse to find interesting things or was SO busy when she was in the woods FOR SO LONG!
She heard Rainbow Dash and Cloud Chaser calling for helping her to clear the cloud until tonight. Twilight agreed and flew up to her, even she has a lot of training to do. After a whole thinking, while helping Rainbow Dash, something tells her that there is something mysterious here in Ponyville and have a clear suspicion that Sweetheart is up to something. She has already planned, when the festival starts tonight, she keeps an eye on her so-called "best friend" and follow her if she decides to slip back into the forest...

At the Midsummer Festival...

Although Twilight isn´t quite interested in the festival, but she wasn´t expected this evening will be something special. She never expected the lanterns floats slightly in the air or hanging on the houses, that can be so beautiful to look, especially the fields in various forms are very beautiful. She walks around to enjoy the good karma around her, she sees other ponies that looked to have fun, especially the young ponies who runs playfully around the maypole.
She looked at Applejack, who sells candied apples and pies with Pinkie Pie. Fluttershy with her animals as a small zoo for foals. Rarity with her new dress inspired by the golden tulips, while delivered midsummer wreaths to happy ponies. And Rainbow Dash, who´s just... Having fun? Everything seemed to be alright as Twilight has no reason to worry about... Well, especially Sweetheart. But it was still nice to see Sweetheart, who´s still there and have fun with some ponies who loved her, even Cutie Mark Crusaders and other fillies, and colts were very extraordinary happy for her.
Twilight was thinking to spand a bit time her, but came straight to Princess Celestia, asking her about the decoration and the festival. Princess Celestia commented how nice Twilight's work has made, she blushed by flatter until she leaves Twilight to meet with Mayor Mare adn her sister, but promises her that they will meet later. But she was most anxious to hang out with Sweetheart and fortunately she is still there.
She was about to meet her, but she notices that Sweetheart had become popular in the last few days. She didn´t mind it all, but she was very happy for her to find new friends, but also misses her. But before she could find one of her friends, she heard Sweetheart calling her and gallops towards her. But then she stumbled over a pony hoof and landed right in front of Twilight.

"Are you okay?" Twilight asked almost in shock.

"I'm okay, it didn´t hurt this time," Sweetheart said in a clumsy tone.

Twilight and Sweetheart giggled and walks along to some stalls with various activities and contests each other like they were competitors, but was having fun at the same time. She always knew that Sweetheart often can be clumsy. Sometimes in Canterlot when Sweetheart came with tea while sitting in the secret library to read books, she often stumbles over books and loses cups and teapot with dandelion tea, and was almost burned. Or when she goes somewhere else in the castle without realizing that there was a staircase and just falls down, where she has sprained her leg and had to stay in bed in almost three weeks!
Luckily she didn´t get any injuries after tripping over a hoof and it was just an accident. But it doesn´t prevent them to have fun in the midsummer festival, especially when they´re dancing around the maypole. Not only she was happy to have her friend on her side, but she was also happy that Sweetheart was still here with her...

Author's Note

I made some changes from my fanfictin account, and also the title. I wasn´t sure about how I should call it. At first I named the chapter "The Festival", but then I realizes that this chapter is about Sweetheart´s mysterious behavior by disappears in the woods or talking to the same stranger (not really happend, but that´s what she´s doing). So I named this title now. I was thinking to name it both, but it would sound stupid.
I wasn´t really sure, if I should find another name or uses the same, but I´ll figure it out later. Also there is three parts as you notices, and I´ll post a picture of Sweetheart in my deviantart and here (if possible) to give you a impression of how Sweetheart looks like. :-)

Edit: I gave the first part a title (sort of...). Very different than my fanfiction account, but I figured that I should give it a another title to explain more about the chapter. It was after I read BrushStroke's "Instant Teenager" fanfic and gave me a idea to the title. :-)