宇

宇 = 于 + 宀 : Yu the Great (yu) just earned her PhD in the space station (Ø3) and is proudly putting on her graduation cap (宀). She was measuring cosmic (宇) rays by investigating the traces they left in a honey jar (于) and is demonstrating her experiment for the camera.

宀 = 丶 + 冖 : Mnemonic symbol: the strokes of this character look like a graduation cap (宀).

Marilyn Monroe (mi-) wants to cook in the anthill's kitchen (an2) but she's afraid of the ants. That's why she builds a bunker: she uses a saucepan lid (冖) as the base, constructs pillars out of petals (丶) and uses a graduation cap (宀) as the roof.

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.