The Mermaid Who Swallowed a Ruby

"Congratulations on your graduation." His young junior stared intently at Harriet with unwavering eyes. The red pupils that met her gaze sparkled and shone like rubies. "I will fulfill your wish, Senior." Why? "...When that time comes, please make me your adjutant." That was a completely unexpected statement. And a few years later, Harriet's 'Ruby' returns as a war hero and appears before Harriet's eyes. . . . "Height 182cm, weight 75kg, a genius who manifested his ability at the age of ten, favorite food is cocoa. On weekends, he mostly reads or enjoys contemplation while sitting in his favorite cafe. For reference, I spend all my weekends observing him. Ah, don't misunderstand. I...