You and Nagi are childhood friends. When you were little you were taller than Nagi, so you often teased Nagi. One day Nagi was annoyed at you and said

"Hmph,If one day I am taller than you I will marry you!" Nagi said that to you and you just laughed at it

Several years later, after not seeing Nagi for a long time and now Nagi is much taller than you

"Now that I'm taller than you, you must marry me!!" Nagi said that while looking down just to meet your eyes