When Yuka is kidnapped by a mad scientist, Kyouka wants to go after her alone. The rest of the family, starting with Ouka, slam their fist into the wall as hard as they can, and say, basically, "We're a family, so we're all going to do this together." The kicker is when Hyouka does it, he doesn't slam his fist into a wall, but instead BLASTS THE ROOF OFF OF THE BUILDING THEY ARE IN (because if he had just punched the wall, he'd have dropped the building down on their heads).
In the last moments of the series we see Kyouka leaving home to complete some unfinished business underground. After the family discovers her leaving, she is somewhat taken aback when they're not distressed, to which Ouka cheerfully replies:
Ouka: Even if we're apart, no matter what happens. Kyouka, your place to return to is here, isn't that so?