It’s the spring of Naho’s second year in high school, and Naho receives a letter from herself, 10 years in the future. The letter accurately depicts what’s about to happen, including details on a transfer student from Tokyo, Kakeru Naruse, who ends up sitting beside her in class. On top of that, the letter also begs Naho not to invite Kakeru out with her group of friends on that day alone, but why?
In other words, this is a new number 
that results from the square root of -1.
.بمعنى آخر، هذا رقم جديد ينتج من الجذر المربع من -1
Kurz gesagt, beim Quadrat
ist die neue Zahl Minus eins …
Es decir, deben encontrar
 un número negativo que...
Es decir, debéis encontrar
 un número negativo que…
Autrement dit, 
le carré de ce nombre est -1.
In altre parole, questo è il risultato
della radice quadrata di un numero negativo.
Ou seja, este é um novo resultado que
 deriva da raiz quadrada de menos um.
Иначе говоря, это число получили
 из квадратного корня -1.