The flute had exactly eight runes – two for the passive effect, one each for the spells, and three foundational runes.
A permanent passive enhancement is a rune formation, which requires extremely deep research.
Other weapons usually use other runes instead, such as hardening, strengthening, sharpening, etc.
Since it's a flute, the foundational runes only strengthened its stability, the conversion of spiritual power into wood elemental power, and a sound rune to transform the winds into sound waves, which is the foundation of the three spells. Although the refined bamboo can do so already, the added rune strengthens this effect and ensures that even those who don't practice the sound path can use it smoothly.
Fengyu had to refine all runes one by one – the refining process was to fill the engraved hidden runes with his own spiritual power and leave his mark.
