Childhood friends can be among the most important figures in an anime character's life - but not every character has them. In fact, some characters don't make friends at all during their childhoods. There can be all kinds of reasons for this, ranging from introverted personalities and social anxiety to being actively shunned by their communities. Many begin to make friends in their teen years, but others wait until adulthood, or never make friends at all.
Perhaps the most famous of the anime characters with no friends is Naruto Uzumaki, whose village turned against him after the Nine Tailed Fox was sealed into his body. A lesser-known example of the trope is Yuki Sanada of Tsuritama, whose social anxiety keeps him from forming connections with people until he meets the eccentric Haru.
Which of these lonely characters are your favorites?
Because Naruto Uzumaki has the Nine Tailed Fox sealed within his body, many residents of Konoha held him personally responsible for the destruction the fox caused, or at least feared that he might not be able to contain it. As a result, he was shunned by the adults of the village, who told their children to stay away from him, and he didn't develop any meaningful friendships until he was twelve.
When she first transferred to her new school, Shouko Nishimiya tried hard to make friends. Unfortunately, her classmates weren't receptive to her efforts and preferred to bully her for being deaf instead. As a result, she grew up friendless.
As a child, Chise's only real relationships were the ones she had with her family - most people couldn't understand all of her magical abilities, and so she was largely isolated. Even her family relationships fell apart of this reason, and it's only when she meets Elias that things begin to change for her.
Thanks to a full time detective job that he's been maintaining since the age of eight, L hasn't had a lot of opportunities to develop his social skills or make friends. In fact, he claimed that Light Yagami, the person he suspects of being a serial killer, was the first true friend he ever made - and he may have been just claiming that friendship to get a reaction out of him.