(Season 6)

This episode is so good I thought it deserved a special page: 

A man beams into Ops hunched over some device.  Kira approaches and asks if he is hurt.  He turns, replies "No, but you will be if you don't do exactly what I say," and seizes her.  She is so stunned she has no chance to move, for the man is the exact double of her dead lover, Vedek Bareil.  He wants a runabout and a chance to escape, and so takes his hostage down through the station to the runabout pad.

She discovers that he is the mirror universe counterpart of Bareil, and completely unlike him.  He threatens her with a disruptor when she stops outside the pad, but she informs him that the power cell is cracked and the weapon is useless.  He moves to attack her but she throws him to the floor with an easy flick.  Kira visits him in his security cell and he realises that she knew the other Bareil, who is now dead.  He guesses that they were romantically involved and apologises for any insensitivity on his part.

Having visited the mirror universe herself, Kira can sympathise with what Antos tells her about his life there.  He admits that he has done some bad things, but hopes that he can escape all that here, having obtained a multi-dimensional transporter to travel to the alternate DS9.  Despite her original misgivings, as Kira gets to know this Bareil she finds herself becoming attracted to him, yet in a different way from how she felt about the Vedek.  But unknown to Kira, the mirror Antos is working with her own double, the Intendant, who has sent him to DS9 to steal one of the Bajoran Orbs.  Having begun a romantic relationship with Kira, Bareil finds himself torn but knows that the Intendant will kill him if he fails.  Acting on a tip-off from Quark, Kira arrives at the Bajoran shrine in time to confront Bareil and the Intendant about to steal the Orb.