1+2=Paradise

For me 1+2=Paradise is something like a predecessor of Kiss x Sis. Both animes are ecchi comedies in which the two sisters harass to the protagonist 

Same basic setting, a couple of (twin?) sisters competing for MC's love. 1+2 is significantly older and has more surrealism, action, and slapstick comedy elements. In the second half, there even is a 3rd woman trying to seduce MC. Kiss x Sis is set in the family home and school environment, with stronger focus on the three mains and less on an actual plot. It's more pervy (not necessarily explicit, no nipples are drawn), but those episodes are mainly found on the OVA.