I was almost scared to open the chapter.
Well, this pretty much settles it :/ Yotsuba was second best girl so not really bad, but c’mon, for the last 112 chapters it was all set up for an harem ending...
Oh, and not a forced one: HERE it would have been not only legit, but also justified by the sisters’background.
So...not really happy about choosing a girl. Imho, Negi considered it for some time but he chose to chicken out midway.