Basically their neighborly feud escalated to the point where Aqua's house was entirely surrounded by berry bushes (planted by both of them) and she can't easily get in or out since they slow you down and injure you.
She then hooked up an underground passage from her house to Shion's to use that as an entrance and exit instead, then later expands it to an underground network spanning the entire main town complete with a fake resistance base and etc. (The irony of her putting immense effort in decorating a fake base compared to her real base was not lost on her)
Shion, with the prodding of her viewers, manages to find the way in, starts snooping around, and Aqua logs in during it, leading to this picture.
As for what happens next, Aqua tries to put some TNT in Shion's home to scare her, but accidentally places it too close to a pressure plate (that Aqua herself put eons ago) and it blows up.Aqua apologises, gets killed, stuff gets rebuilt, they shake hands, and Shion gets allowed access to the Aqua Line now. But both sides still put in some traps and pranks afterwards.
