Koori no Reijou wa, Outaishi no Amai Dekiai de Tokasareru

Sophia, the daughter of a marquess, has been strictly raised from childhood to believe that “a noble lady should never show her emotions."
As a result, Sophia always has a blank expression on her face, which causes her to be shunned by other people at school.
One day, Sophia meets a foreign student named Felix. He notices Sophia's true feelings hidden behind her expressionless face, and he becomes her confidant.
As time goes by, Sophia wishes to express her gratitude to Felix and her special feelings for him…

The two of them become closer as the young woman known as “The Iron Mask” opens her heart to a boy for the first time, and her world begins to shine with vivid colors.

(Source: Comic Room, translated)