Osamu Yasuhara first appeared as a client of SPR; as the president of the student council, Yasuhara urged Naru to investigate strange happenings at his school. It was Yasuhara's persuading (and the petition he had orchestrated) that convinced Naru. Yasuhara was a great help to SPR during this time and was employed in later cases for help with research.

Yasuhara's schoolmates nicknamed him "Echigoya" (the name of a very old Japanese store), which is a very good indicator of his personality. They say that he has the smile of an old man--innocent, but one never knew what was lurking behind his face. Yasuhara is a very cheerful and helpful person, who gets along with just about everyone. Even so, he is constantly making jokes, particularly with Monk. In Vol. 11, Mai comments that her favorite thing about Yasuhara. His joking, even in serious situations, makes her feel like everything will be all right.

Another defining trait is Yasuhara's intelligence. Japanese seniors are usually consumed with entrance exams for college; they are placed on shorter school schedules and do not have much time for extracurriculars. The fact that Yasuhara managed to be president of the student council is very impressive and remarked upon by several characters in Vol. 4. He frequently serves as the primary researcher of SPR. In his first case, this is justified, as he is the only one who really knows the students, but this role is expanded in volumes 7, 9, 10 and 11. In addition, Yasuhara is shown to have good perception.

as reference for his voice: https://youtu.be/fZF8VeJr2co keep watching though its funny