(of time or place) in; at; on / (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for / (indicating a source) from; out of / (used in comparison) than / (used in the passive voice) by
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.
雾
=
务
+
雨
:
Willy Walrus (wu) has a special task (务) to fulfill in the space station's bathroom (Ø4). With a vaporizer he is creating a lot of fog (雾) which will slowly form a cloud and result in rain (雨). Willy will collect the rain and vaporize it again. With this experiment he is doing an important contribution in understanding the world's climate system.
之
=
丶
+
Z
:
Mnemonic symbol: Sooo sleepy... "zZz" (the character looks like a "Z"). James II of England (zh) fell asleep in front of the space station (Ø1). He sleeps on a big petal leaf (丶), making loud "zZz" (之) sounds.
中
=
丨
+
口
:
Mnemonic symbol: a dart board, because you always try to hit the center.
Julian Giant Squid (zhu-) is throwing dinosaur bones (丨) as darts on a dart board in front of the engine ((e)ng1). To make it a bit more difficult he's throwing mandarins (口) into the air as well and skewers them up right in the center (中 is a mandarin skewered on a dinosaur bone) in mid flight with the dinosaur bones. He's still able to consistently hit the center (中) of the dart board.