Setting and Story
Child Mikuo opens clock to find Miku inside. She is by his side as he grows up to be an adult, working on clocks all the while. He's also in bed a lot, so his health isn't the best. Cloaked people with swords arrive one day. The leader in the long cloak give Mikuo a card with designs for the large clock. He's then shown to be working inside the clock. Miku is there, probably helping him out by handing him tools or wiping grime off his face because working inside a giant clock can be dirty.
Mikuo notices a ring in the clock. The clock gears are moving freely behind it. On his finger is also the same ring. He closes the door and leads Miku away by the hand. It's later revealed that he sabotaged the clock.
Miku is then seen wearing part of his ring as a pendant while killing the cloaked people and destroying the clock tower with part of the clock. There is emotion in her eyes, and she's taken some damage from her fighting.
She recalls Mikuo as they walk the stairs to the door. They are followed by two of the cloaked people. Miku and Mikuo reach further inside to locked part of the actual clock. Mikuo looks like he's explaining something to Miku when he sees the two cloaked people. Miku is about to be attacked when Mikuo pulls her out of the way, taking the blow instead. He's partially if not fully blinded. (He appears to be looking at things later in the PV.) Miku then attacks the cloaked people; there is a little blood on her hand. Mikuo is shown to be in a lot of pain, and Miku brings Mikuo back home to bandage his eyes with a blindfold.
The cloaked people come for Mikuo (and Miku eventually since she's a witness), and Mikuo notices them outside. He coughs and collapses a bit onto Miku, either from his injuries or illness. However, he then goes to hide Miku back inside the clock. He winds the key in her neck and stares at her, perhaps debating on what he should do. Miku goes to wipe his face. His expression softens for a moment; then he embraces her, smiles, gives her the key, and shuts the clock.
During all this, Miku is starting to truly come alive rather than being just a doll or mechanical being. The clock doors open a crack, and Miku sees Mikuo killed by the two cloaked people. The two cloaked people leave, not knowing Miku is hiding in the clock. She tries to "wind" Mikuo up again, back to life, but since he is not like her, nothing happens.
Miku looks at the clock tower with a distasteful expression, takes Mikuo's ring, and goes to attack the clock tower and the cloaked people. This is back to current time, and Miku slashes at the clock. The mechanics that were once spinning freely behind the other ring are shown to be now jammed with fabric, Mikuo's doing earlier.
As the clock tower crumbles around her, she hopes to see Mikuo again. The two are shown reunited: Miku full of life and Mikuo with a blindfold. They smile, hand in hand.
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Mikuo Hatsune: History
Mikuo is from a long line of clockmakers, the Hatsune Clockmakers. The earliest of them had constructed the giant clock tower in the town where Mikuo lives. They passed down skills and heirlooms from generation to generation. This included the clock bed with Miku inside (most likely the house was passed onto the next generation, including the bed), a ring that could split into two, and a key. The names Miku and Mikuo are names passed down as a tradition. The Hatsune line also had a dark spot in their past. The clock tower housed a dangerous mechanism. The gears of the clock fed it energy; as long as the clock ran, the mechanism would be powered or something. Or maybe it granted some other power that could be dangerous in the wrong hands and sabotaged so no one could access it. It's unknown, lost to time only to be discovered by the cloaked people. Considering that they were willing to kill for this, they have high goals and shady morals.
Mikuo started learning the clockmaking skills from his parents at an early age. However, he was often sickly and stayed in bed a lot. Miku brought things to him to work on. At some point early in his life, his parents die "from an accident" when working on a project. Mikuo explains to Miku that his parents are like a magnetized clock; they don't work anymore and can't be repaired like Miku can. However, Mikuo never felt lonely as long as Miku was around. He would teach her all he could and considered her a very dear friend and some really important to him. Mikuo didn't treat her as a thing but a person.
He continued to learn about clockmaking through his parents and ancestors' notes. The notes were in a special code, something that the cloaked people couldn't understand. When they discover that Mikuo has learned the tradition of the other clockmakers, they approach him. The card the leader holds is written in the code. Eager to learn more about his family's work, Mikuo agreed. It was hard work for him as he wasn't used to the effort, but he did it gladly.
That was... until he saw the ring embedded in the device, the same as the one he wore. Mikuo started to suspect things weren't as it seemed and that perhaps his parents hadn't died in an accident. Mikuo continued working on the clock, to discover its secrets, discover just what he was working with, but before he left, he jammed that mechanism, so the clock wouldn't work. As the fabric was behind a special locked panel, the cloaked people remained unaware of this for some time.
Then one day, Mikuo and Miku were followed, and the cloaked people realized Mikuo's sabotage. They planned to use Miku as leverage for forcing Mikuo to finish the work. However, Mikuo became blinded, and Miku became a force to be reckoned with. Miku knew the dangers of the clock tower. Mikuo told her everything after all.
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Mikuo Hatsune: Personality and Other Facts
Mikuo sings while he works on clocks, though he's not a great singer. He's very quiet and has to sing slowly to simple tunes as he'll run out of breath too easily. His singing tends to be more of a lullaby quality because of this. He's not used to an audience beyond Miku.
Similarly, Mikuo cannot fall asleep without the sound of a nearby clock. It's just not possible as a doctor found out when he tried to prescribe him rest in the countryside away from clocks. (The idea was to give him a holiday away from tinkering on the mechanics.) The retreat was very short and never tried in such a fashion again. In hindsight, it should have been expected; he sleeps in a clock bed.
His favorite food is leek and potato soup, with extra leek. It helps warm or cool him as it can be served both ways, and soup is always easy for him to eat when he's not feeling well.
He has also been sick his entire life as his family members before him. It's some hereditary condition.
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