101Leafy researched the games.
Mirage Finsword

Chameleos-like invisible sword. Good for hit jobs. Requires Guild's OK to own.
An unusual long sword that applies the traits of the "Mist Dragon" Chameleos to its blade, so the whole blade can vanish from sight. Because of this, it is sometimes used for assassinations, and owning one requires permission from the Guild. Even hunters who are given permission must keep the sword under strict control.
Our translation of 復刻 ハンター大全 (KADOKAWA / Enterbrain, 2014), page 149.
| Class | Long Sword |
|---|---|
| Rarity | 5 |
| Attack | 816 |
| Affinity | 10% |
| Defense | +8 |
| Slots | 1 |
| Table price | 35,000z |
Upgrades
| Upgraded from | Iron Katana "Gospel" |
|---|---|
| Upgrades into | Mirage Finsword+ |
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 692.
Materials
Chameleos Horn ×2, Chameleos Hide ×5, Chameleos Tail ×2, Dragonite Ore ×8