From the first chapter it may look like this manga is about a nasty teacher into shota-con, however that is only the Very Very beginning and shota-con has nothing to do with the story at all. That first occurrence is needed only to bring the two main characters closer together to prepare for their journey of life together.
This manga is one of the best I have ever read; it will make you smile with joy and bawl your eyes out from beginning, when they are just children, to the end when they are old men preparing for rest.
It shows the very seed of
true love and how it conquers all despite all of the "complexes" that come up in one's life. The main characters may have a few falling outs, but as the red string predicts (metaphor), true love will prevail.
This is one of the most serious mangas I have had the joy of reading and one of the only ones I've seen that showed main character's life from beginning to end. It is heartwarming and even if the beginning throws you for a loop, once you get past that you will never regret sticking with it.