Yanda

Background
Koiwai's and Jumbo's friend who is a year or two younger. His name was first mentioned in the manga's debut issue during the time when the Koiwai's have just newly moved-in to their present home. Jumbo was there to assist them in the transporting and the sorting of their belongings while Yanda failed to take some time off work that would have enabled him to offer help to the Koiwai's. At that time both men agreed that he was indeed useless/unreliable.

Yanda would eventually make his initial appearance during the 30th chapter. Often depicted as a white-collared office worker who normally sports a coat with tie, his boyish facial features coupled with his wild-styled dyed hair somewhat contradicts the way he dresses. Although he drives his own car, he lives from paycheck to paycheck since his salary is on a monthly basis. This makes him short on cash most of the time hence his dependence on convenience store food for nutrition.

He often visits the Koiwai's in order to get free hot water for his instant ramen and also to hang out with them if he has time off from his job. These interactions often evolve into comical situations, especially at the expense of Yotsuba or himself, and would be plot spring-boards for later chapters.

Relationship with Yotsuba
Yotsuba's "mortal enemy" in the series, Yanda seems to always get on the five-year-old's bad side. He seems to like Yotsuba in his own way and is often asking her to play with him, but, due to their unfortunate first meeting and Yotsuba regarding as "suspicious", she always answers: "NO."

In contrast with the other characters' kind and considerate approach in spending time with Yotsuba, he behaves like a bratty, pompous man-child while dealing with the little girl's naivety and innocence.

Most of his visits to the Koiwais involves childishly competing with Yotsuba using tit-for-tat pranks in order to one-up the other. This includes taunting using silly imaginary feats, teasing with food, getting in each other's way, and generally just not being very nice towards one another.

While sharing scenes with him, Yotsuba is easily annoyed and prone to saying offensive language such as damn, bastard, and the like to humorous effect. He eventually began showing his good side during the Pancake chapter when he became supportive of Yotsuba's culinary efforts and the Bubbles chapter when he was generous in lending his instruments to her.

It would be notable to add that Yanda did try to be nice and reasonable to Yotsuba during their first meeting, he was just rubbed the wrong way due to the titular character's distrusting behavior when interacting with strangers; their relationship still borders on love/hate but it has gotten better as of late. Yotsuba thought that since Yanda was suspicious she didn't let him in her house, so Yanda dropped candy on the ground for her to pick up. When Yotsuba saw him she slammed the door on him, which led to other scenes Yanda being Yotsuba's mortal enemy.

Relationships with Other Characters
Koiwai and Jumbo often enjoy siding with Yotsuba by calling Yanda a bad guy and an unreliable person much to latter's chagrin. His two friends would often tease him quite a lot during their capers (aside from labeling him like a delinquent and/or an idiot, they once pressured him into believing that he was going bald) but the three of them seem to get along very well. It was also mentioned that he was Koiwai's "kouhai" (underclass-man) at one point during their schooldays when they were younger.

Like Jumbo, Yanda also finds Asagi very attractive and even asked if she was a model; he acted out-of-character when introducing himself to her. Unfazed when Jumbo told him that Asagi may already have a boyfriend, it was later revealed that he has a girlfriend but Koiwai deduced that they may have broken up because she would not return any of Yanda's calls.