Yoshiyuki Terada is a teacher at Tomoeda Elementary School. During the series, as the main characters go through fourth grade, and enter the fifth grade, he acts as their home room teacher. He is also shown teaching in other classes, including the physical education classes, and he acts as the chaperon on school several field trips. As the series progresses, it is revealed that he is having a romantic relationship with his student Rika Sasaki. In the manga, they become engaged when he gives her a ring, noting that he hopes it will one day become her wedding ring. Rika gives him a teddy bear she made and named after herself, which legends says will allow them to remain in love forever. Towards the end of the series, when Sakura is unsure of her feelings about Li, the couple is shown having a picnic at a park, with Terada slipping away so Sakura doesn't notice him. During the series, none of the other characters appear to know about the relationship, though when Rika is taken over by the Sword card, Sakura hears her call out "Sensei" (teacher) when she uses the illusion card to show Rika her most beloved.

In the anime adaptation, their relationship is not shown in the same light. Their engagement and more romantic scenes between them are removed, and Rika notes that Terada reminds her of her absentee father. Terada is also shown accepting cakes made by Rika and in accepting the bear and naming it after his "hardest working student." In the Cardcaptors English dub, he is simply called Mr. Terada, and all aspects of the romantic relationship between Terada and Rika are completely removed, with Rika's shyness and reactions to him made to appear to be more of a general fear of men than romantic feelings.

In the anime series, he is voiced by Tōru Furusawa for the first season and first movie, and by Katsuyuki Konishi for the second and third seasons and the second film. In the Cardcaptors dub, he is voiced by Brian Drummond.

Source: Wikipedia.