Bongseon (봉선, Bong-Sun) is a National Treasure currently wielded by Yu Mira. This National Treasure is a sword. It was stolen by Nox but was retrieved and returned to Mira after she successfully passed the National Treasure Certification Exam.
Before it was awakened it looked like a typical wooden sword used for training. When awakened it took the form of a long sword with the Yin-Yang symbol at the hilt but later changed after she recovered the sword. It now appears to resemble a red thin katana.
It has the normal abilities of a sword and like most National Treasures it is impervious to Charyeok attacks and can give the user more destructive force, among other abilities.
- Teleportation: It is capable of teleporting to its owner. It appears to have no set distance and will appear either when called or needed.
- Levitation: It has also been seen levitating and coming to its owner on command.
- Attack Enhancement: It is capable of enhancing attacks and cutting through powerful Charyeok easily. It is also capable of blocking extremely powerful attacks.
- Charyeok Amplification: It also amplifies a person's Charyeok but this function can only be used three consecutive times for an unknown time period.
- Bongseon is the courtesy name of Yeo-Po.
- Bongseon (Hangul: 봉선; Hanja: 奉先) means "In Reverence of Father's Wishes", befitting of Mira's character, especially in the first half of the story where she felt like she had to carry the burden of her father's wish to find a worthy successor of the Moon Light Sword Style.
- There is a real Korean National Treasure called Bongseon Honggyeongsa. It was a stele of the the Bongseon Honggyeongsa Temple. However, this has nothing to do with this weapon, they just coincidentally have the same word in the name.