マルベリー
from Older Elite Knight Is Cute Only in Front of Me (Manga)
Mulberry first met Haru 3 years ago before the story takes place, after the Knights' Academy's entrance ceremony concluded. They bump into each other again when she's looking for someone to accompagny her at her senior's wedding and Haru goes with her as he knows Karen too will be there.

Older Elite Knight Is Cute Only in Front of Me (Manga)
I the strongest prodigy of the kingdom, Haru (16) have been assigned to the Knight Order. My surperior in this knight order, where the strongest of the kingdom gather to become the elite, is Karen-san, a 29 year old single woman. Usually she is a feared and noble... The Karen-san that does things like, inviting me to her room, acting like a spoiled child or showing special facial expressions only towards me is just too cute...!

Older Elite Knight Is Cute Only in Front of Me (Light Novel)
I the strongest prodigy of the kingdom, Haru (16) have been assigned to the Knight Order. My surperior in this knight order, where the strongest of the kingdom gather to become the elite, is Karen-san, a 29 year old single woman. Usually she is a feared and noble... The Karen-san that does things like, inviting me to her room, acting like a spoiled child or showing special facial expressions only towards me is just too cute...!