Okay I'm not seeing the 'implied futanari' or the 'yuri' in this removing both and adding 'masturbation' If the artist tagged it as such than you can add it back but the source is just the image so I cant look at the original tags.
The artist has gotten extremely lazy with the tags so there isn't much to go off of if you use tags only. Here though we tag what we see and what we see is Vert sitting on top of Nepgear with a pleasured look on her face. So I think at least the yuri tag is appropriate here.