 If you liked Kiss x Sis (TV) |  ...then you might like Isekai One Turn Kill Neesan: Ane Douhan no Isekai Seikatsu Hajimemashita |
These two animes are only related to one strong aspect that is onee-san loving their younger brother in a romantic way and wants to make their relationship more than just siblings. Only the main theme of these animes are connected, other than that they are totally different. As "One-Hit Kill Neesan" is an isekai action anime (not much ecchi) and "Kiss x Sis" is a romance-drama (100% ecchi) anime . But there might be another thing similar, both of them can be described as Harem.