Eren and Mikasa's flashback was jolly good. Such a psycho couple.

I reckon Mikasa is so strong partially because she keeps her head really cool, isn't afraid (except for Eren's safety) and doesn't hesitate. Fighting against these giants, the first attribute is quite essential, as we saw in the previous ep when Eren's squad was annihilated largely because Eren is always so hot-headed. It's not like most of the giants we have seen would have been overly intelligent. So, humans ought to use intelligence to defeat them. However, Eren threw such things to the wind and charged forward heedlessly. The first titan we saw Mikasa defeat was doing the exact same thing Eren did, and paid the price similarly when Mikasa disposed of it before it knew what hit it.