There's a violin track in Naruto Shippuden that's kind of sad or emotional. It starts with a little guitar or banjo, then continued with a violin.
Up until season 18, most of the time the song comes up in a flashback, like Obito's flashback, and in the storybook from Jiraiya, and even more of them. One example is in episode 440 in the book from Jiraiya, the song starts at 17:17. Another example is from episode 464, around minute 17.
I have checked all the OST, but I couldn't find it.
What is the name of the song?