Yoshimo

Yoshimo is a true neutral human bounty hunter, a class kit for thieves and he is a potential companion. He will join the party in Baldur's Gate II: Shadows of Amn when they reach the second level of Irenicus' Dungeon in order to escape the dungeons. He has the following items when joining the party: a katana +1 which can only be used by him, a short bow, studded leather armor and some arrows. He is not available in Baldur's Gate II: Throne of Bhaal due to plot reasons.

In-game description
"When asked about his past, Yoshimo seems disheartened that you are not acquainted with his reputation. By his own account, he is apparently well known among the people in the know,  both as a daring rogue and a dashing man about town. While the story sounds impressive, he seems ungainly for such exploits, possibly a bit more hapless than debonair. He wears it well, however, and perhaps even capitalizes on it. He seems to know that his kind of good-natured humor is well appreciated by most everyone he meets."

Baldur's Gate II
When you reach the second level of Irenicus' Dungeon, you will see Yoshimo. He claims he also an escaping prisoner. It is wise to recruit him as he can see what others cannot and is a very skilled thief,

If Yoshimo is in the party when you get inside the Asylum, after a tour of the prison cells Jon Irenicus will reveal himself and will also reveal that Yoshimo is his puppet and has been using him all along. The party will speak of their disgust over this betrayal. Yoshimo will then leave the party and Imoen (who was previously held prisoner) will return and join you.

After escaping Bodhi's labyrinth, Yoshimo, under the orders of Irenicus will attack you along with some other rogues. Also, Irenicus has somehow cast a geas spell upon him, which forced him to obey Jon's will or die instantly, which makes it unavoidable to kill him. You can take his heart to a priest of Ilmater, to grant him rest in the afterlife and you will also earn 200,000 xp for doing so.

Quotes

 * "Fear is for those of no confidence!" (during battle).
 * "All the world is blind to my passing." (when invisible).
 * "Be doubly careful. I'm sure all manner of stupid mousetraps await our toes in the dark."
 * "Where shall I display my skill and expertise?"
 * "Hiiiii yah! Heh, tourists love that stuff."
 * "If memory serves..."
 * "Soo desu ne?"
 * "I am ready, I think."
 * "What do you need? I am skilled in avoidance."
 * "You require my counsel, yes?"
 * "Ah yes... the city. With all its people and their accumulated wealth, yes?"
 * "Yoshimo is willing."
 * "Kia!! Yeah." (when making a critical hit).
 * "You require my counsel, yes?"
 * "You're right behind me, right?"
 * "Very well. Hii - yah."
 * "Yokatta."
 * "Nothing dangerous, I would hope."
 * "I can dance on the head of a pin as well."
 * "Fleet on foot and all that."
 * "I must have rest soon, my friend. I have no wish to be weary when my skills call for careful concentration... (when tired)."
 * "My thieving skills will be of little use here. What wealth does a bear drop in the woods?" (when in the wilderness).
 * "I am not worried. I am sure these...setbacks are only temporary." (when reputation is too high or too low).
 * "An odd choice. Have you been hit in the head with a rock, as of late? I? In the front? Well, it is your call..." (when made leader of the party.)