非必需

非 = 三 + 丿 + 丨 : Mnemonic symbol: a negative film (photography).

Frankenstein's monster (f) made an effort to photograph the Eiffel Tower (ei1), but now his negative (非) is a big mess. In front of the tower he set up a camera on a Cartesian coordinate system (三) as a tripod, and he attached a banana (丿) and a dinosaur bone (丨) to the camera so that he can finely tune the angles. All was for naught as he now holds the messed up negative in his hands.

必 = 丿 + 心 : Mnemonic symbol: 忽必烈 [Hū​bì​liè​], Kublai Khan. Certainly (必) Kublai Khan (必) has to keep face, but he cannot hold it any longer. In the space station's bathroom (Ø4), He absolutely has to (必) tell Brunhilde (bi) his love for her strong character and offers her his heart (心). Brunhilde is a bit embarrassed because all she has to offer in return is a banana (丿). Kublai Khan feels like his heart has been crossed out (the 丿 stroke is crossing out 心 in 必).

需 = 而 + 雨 : Mnemonic symbol: When it rains and you do not want to comb your hair again, you need a rain cape.

需 = 而 + 雨 : It is raining in front of the rain station. Because Xu Xian doesn't want to comb his hair again, he uses a rain cape to stay dry.