In the pixiv comments, someone asks...

フーミン6/5/2014 22:47

扉のところいるのは武蔵かな？

"Is that Musashi over by the door?"

The artist replies...

ピー6/5/2014 22:59
> フーミンさん

正解です！ポートワイン破壊作戦から帰ってきて島風の様子を見に行こうと思ったら天津風もいたのでカステラ押し付けて自分はこっそり様子をうかがってる感じですね。

"That's right! Returning form the operation to destroy Port Wine, Musashi decides to check on how Shimakaze's doing only to find Amatsukaze already there, so she's pressed the tray of drinks and castella she brought on Amatsukaze and is quietly watching over them."

Tomodachi Tsukuru... Let's make a lot of friends, or what? I'm not good so someone please put on the note.

Probably something to do with Shimakaze not having sister ships and how Amatsukaze is meant to be her friend