There's not Much Else to It
Princess Celestia got out of her bed, her eight legs tapping over the floor and her three pairs of eyes lazily twitching open as she made her way towards the balcony to raise the Sun. She got out, the cold air of the early morning ruffling the fur on her back, and raised the Sun as she did every day. She then walked out of her room and headed down the corridor to where she would have breakfast with her sister. The guard in front of her room passed out from shock when he saw a giant spider walking through the door he was guarding.
Celestia entered the room, ignoring the look of utter incomprehension she received by a maid who had dropped her duster upon seeing her in the corridor. She sat at the table and began to move her fangs in anticipation.
Luna walked in the room shortly after. Her first reaction upon seeing the creature was to stop and stare, wide eyed and unsure of what was happening.
This gave the spider enough time to lift her head and notice her. "Hi Luna," Celestia merrily said.
"...Hi sister," Luna said after a brief pause, still confused as to what was going on. She slowly sat at the table and studied the non pony in front of her.
"So, did anything interesting happen tonight?" Celestia asked, beginning to sink her fangs into her meal, melting it with her venom and then sucking it up in her mouth.
"Nothing," Luna replied, "how about you? Is there something you feel like you should tell me?"
"No," Celestia answered as she moved on to the next plate.
Luna gave a brief cough. "Are you sure, sister?"
Celestia stopped eating. "Am I forgetting something?" she asked with a worried gaze. She started to distractedly weave a web with her legs while concentrating on what she could have forgotten.
As an answer, Luna simply stared at her body, giving a few small jerks of her head to signal she was pointing at her.
"Have I forgotten my crown again?" Celestia moved a leg to check above her head, concerned.
"Is there... really nothing that seems out of place to you, sister?" Luna asked.
Celestia stared at her reflection at the bottom of the metal plate, all six eyes staring back at her. She watched each one of her eight legs, then studied the web she'd weaved. Then she looked at Luna. "No, not really. Well see you later, Luna, I have duties to attend to."
The large white spider walked up to the nearest wall and then up said wall, then made its way to the room's other side by walking on the ceiling and descended back on the floor to exit the room through the door, leaving a very confused Luna behind.
First in the list of things Celestia had to do that day was an inspection of her guards, so she headed to the large hall where she knew they would be waiting for her. On her way there she caused panic attacks to a large number of ponies, who had not been informed that their ruler was now a disproportionally large arachnid. She finally arrived at her destination, but found the door locked from the inside.
On the other side, a guard grunted as he pushed against the door to keep it closed. "A giant spider!" he said, gritting his teeth. "When she said she wanted to inspect us I didn't think she would release a monster in the castle to see if we could keep it out!"
"Well at least we got some action rather than a boring examination," another guard replied.
Celestia banged multiple times against the door, even trying to push it open with her magic, but the guards on the other side kept it tightly shut. She was about to request them to open it, then a flash of realization hit her. Of course, it was obvious. They had decided to show her they were prepared to deal with any danger by demonstrating their ability to keep even her out of a room, thus sparing her the slow and boring examination. "My compliments to you, you demonstrated your abilities quite well," she said to the guards behind the door before leaving, the steps of her four pairs of legs cacophonously resonating down the hallway as she crawled up a wall.
Having gained some free time, she decided to pay a visit to the library. The librarian threw herself behind the counter as she saw her approaching, and Celestia was free to crawl on top of a bookcase and grab a book before weaving a large web between two columns and nesting herself in the middle of it.
"Princess Celestia?" Twilight called as she rushed into the library.
Celestia lifted her six eyes from the book to look down at Twilight, who stumbled backwards upon seeing her. "What is it, Twilight?" Celestia asked, hanging upside down from a thread as she lowered herself to the ground.
Twilight struggled to begin her speech. "You see, Princess, Luna informed me of some rather, well, bizarre events that you appear to have been involved in, and she requested my help in explaining the situation to you, as you appear to be oblivious of it."
Celestia looked perplexed. "What has happened? I assure you, I haven't noticed anything out of the ordinary."
"Well, how can I say it..." Twilight hesitated for a bit, then she levitated a mirror from a side of the room and placed it in front of Celestia.
"I don't understand," Celestia said, looking at herself, "is my mane not properly arranged?"
In that moment a guard came running into the library, his breath ragged. "Princess," he said between pants, "there have been reports of-AAAH! A GIANT SPIDER!" he screamed as he finally looked at Celestia.
The princess turned towards him. "A giant spider? Where?" she asked, looking around, seemingly a little worried.
The guard passed out.
"Hem, Celestia," Twilight called, "I think he was talking about you."
"Me?" Celestia looked over herself. She studied her reflection in the mirror. She carefully observed her eight legs and six eyes, as well as the structure of her body. "Oh. It would appear I am, in fact, a giant spider. Curious. I guess I need to do something about it."
Twilight smiled. She was about to say something but Celestia interrupted her.
"Dear citizens," she spoke, her voice magically amplified to be heard by everypony, "I would like to inform you that your princess is now a giant spider. You can now resume your activities, thank you for your attention." She then went back to reading her book in the middle of her web, leaving a perplexed Twilight and an unconscious guard behind.
