Prologue【A letter】

Avalonis, a huge modern school city with many schools and research institutes gathering together, which is ruled by the federal government. In Avalonis, you can find over 100 schools, including kindergartens, primary schools, secondary schools and high schools. With research institutes' research developments, the technology has developed very fast within 30 years, becoming the city ​​with the highest technology in the world.

In the afternoon , Zero was walking around the street, while eating the hamburger he bought from a food truck. In the usual days, he was supposed to practice with his friends, Miki, Tsukasa and Saiba since they are the members of the band -- "CloverHearts". However, those three were busy with their personal work, so they decided to cancel the practice today.

Thankfully, it was not like that often during the summer vacation, so they did not have to worry about the training course or paperwork.

But now, Zero has nothing to do. "Ahhh... I feel bored. Dad is now working in the studio and Abby is probably busy with her concert schedule."

"Still no gains from the search, it's been almost 7 years, and no results." Zero sighed while looking at his phone. "Sigh… I wonder where it goes…"

Since it's a holiday, Zero decided to go back home, take a good rest from these busy days.

Just when he arrived home.

"What's that?" Zero found a mysterious envelope when he checked the mailbox.

There are some words on the envelope

"For Nanairu Zero"

"Top secret"

"Do not dismantle"

Zero picked up the envelope , staring at these words, he couldn't find the name of the sender, but surely this letter is for him.

He opened the envelope, carefully taking the paper from the inside, and read the message on it…