A new student arrives from Russia on exchange, immediately confessing her feelings towards Moroha. Moroha is accommodating, but Shizuno has suspicions.
I'd heard from a reputable source 
that there's a tradition
Eine glaubwürdige Quelle teilte mir mit, dass es …
Una fuente confiable me 
dijo que en Japón tienen
Una fuente de confianza me 
dijo que en Japón existe
D’après une source fiable,
Ho saputo da una fonte attendibile che
De acordo com uma fonte
 confiável de informação,