Nise Seiken Monogatari: Osananajimi no Seijo wo Uttara Michizure ni Sareta

Story

My childhood friend, Magary, was chosen to be the saint. From here on out, she'll have to maintain a smile at all times while at the royal capital and take lessons in etiquette and dance. She'll be living in an excruciatingly stifling world. Having been together since birth, there was naturally one thought in my mind. While feeling a little bit of loneliness… I pushed my childhood friend (who was trying to escape with all her might with her arms still bound) towards the knight that came to pick her up.

Synopsis via AniList (English).