Yoshimo's Katana

Yoshimo's Katana +1 is like an ordinary katana +1, but this weapon is enchanted in such a way it can only be used by Yoshimo. This item appears in Baldur's Gate II and is very likely to appear in Baldur's Gate II: Enhanced Edition as well. This weapon is in the possession of Yoshimo when he joins the party.

In-game description
"Yoshimo's Katana +1: This blade, although only lightly enchanted, has achieved a semblance of awareness, enough so that it allows only the thief known as Yoshimo to wield it.  Any other than he cannot use this flawless katana in battle."