This works pretty much identically to Suikoden weapon sharpening. Level 1 Weapon Strength is calculated as 10% of a character's strength at Level 1. Levels 2 through 6 add that much to your strength. At Level 7, the weapon's name changes and, up until level 11, adds 15% of your Level 1 Strength. At Levels 12, the name changes once more, and from there until Level 15, the weapon level cap, you get 20% of your Level 1 Strength. To sharpen to the next level costs 250 canu multiplied by the current weapon level (this number may increase as I finish balancing out canu gain).