101Leafy researched the games.
Kirin Thundersword

A blade that harnesses lightning and unleashes it into your victim's body.
| Class | Great Sword |
|---|---|
| Rarity | 5 |
| Attack | 624 |
| Thunder | 550 |
| Slots | 0 |
| Price | 20,000z |
Upgrades
| Upgraded from | Executioner |
|---|---|
| Upgrades into | King Thundersword |
Can also be made new at the smithy.
Upgrade tree from モンスターハンターポータブル 2nd G 公式ガイドブック (Enterbrain, 2008), page 680.
Materials
Kirin Horn ×7, Kirin Mane ×2, Rubbery Hide ×2, Lightcrystal ×3