A (very) loose translation might be "Big Sista". It's how younger members in a female gang address their boss. It's sort of a hooligan's version of aneki.
Kourindou-san.That would be acting too much like a stranger though...Maybe I should just go with his given name like usual?...Haa, what the heck am I doing now, even though we've been acquaintances for so long.
Maybe it's hopeless already.Anego, don't give up!Ugh...I can't go on. Guys, I leave the rest to you...Pull yourself together, Sunflower D!He is a similar being to you, it must be that it takes some time to conquer him.Rinnosuke-san.Kourin!!...No, that's no good, it's too much like that black-and-white, and it's out of character for me....That doesn't give a good image at all. Rejected.Anego's so depressed! Damn, at this rate, we're going to die!