Tatenashi dragged Houki to the shower room by pulling her hand, and this reminded her how Tabane always did the same thing in the past (pulling her hand, bringing her around). Houki monologue how she feels about Tabane: that Tabane is "an existence like a wall that she can't overcome"; "Someone that she can rely upon, and be proud of"; "A difference living thing, with a different talent"; and lastly "A person that she adores, up until a certain 'Incident' ".
Regarding this "Incident", it was a memory that Houki sealed in her mind. Houki blamed herself and not Tabane, and she thought that she hurt her sister. She also indicated then when she was young, she's already drowned/indulged in power. She's been avoiding Tabane since because of this 'event'.
Finally, Houki is thankful to Tabane because of Akatsubaki. But because she just couldn't figure out what Tabane is thinking right now, she is scared. Skip to epilogue, Tabane said Houki is strong, just like "that time"
People should not be surprised at how strong Houki is, but rather be worried what with the haxing thing, and who knows how hax it will be when Akatsubaki goes 2nd Shift (Block a
colony gigantic laser? Destroy missiles by just pointing finger? or maybe hijack all the IS cores and make them do Morning Musume dance?)
Can I have Maaya Sakamoto to voice Tatenashi :P