Segawa and Sachi are both good options but as per Nisekoi theme, I can feel the author will use some lame excuse to win the bitch :'( I did ship Chitoge but here Erika is a pure annoying girl.
Why I think sei father is cruel hearted person? I mean his wife loves him and stay faithful to him atleast try to get your mess together and love your wife.
Some might say Eren's reason for killing all people of the world is childish but just put yourself in his place "what will you do?". Some righteous people will reply we will work together not kill each other but that's an ideal world point of view like in a fairy tale or one-piece type of world...