不必

不 = 丆 + 卜 : Bruno Bear (bu) is setting up a wind wheel (丆) with a voodoo staff (卜) in the space station's bathroom (Ø4). He also puts a "forbidden" sign (mnemonic symbol for 不) on it, to make clear that it may not (不) be stopped.

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).