於心不忍

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.

心 = 乚 + 丶 : Marie Curie (xi) uses a shovel (乚) to dig a hole in front of the encampment ((e)n1). She wants to bury her heart (心). To the side are three petal leaves (丶), with which she wants to cover it afterwards.

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.

忍 = 刃 + 心 : Robinson Crusoe (r) cannot endure (忍) life anymore. In the encampment ((e)n3) he puts his heart (心) on the floor and is ready to end his life with one streak of his bihänder (刃).