This Saber is a male while every single "father" Mordred has previously has breasts (small but still count) so she can not accept. Also the pun between "father - chichiue" and "breasts - chichi" which explained in the translation.
Hhhhhhnnn Hnn-Hnnnn♪Hm!? This feeling is...!Father!!How can you be Father if you don't have any tits!
Father(Chichiue) and Breasts(Chichi)Hello, Mordred.The you in this world is quite energetic too.Fucking bastard! Who the hell are you!!!?Ehhh!? It's me, Arthur!!Ti- What!?