The robot (大) and the Queen of Hearts (qi) reached an agreement in the space station's bathroom (Ø4). Lacking a proper pen they sign their written deed (契) with an engraver (㓞).
tree / wood / coffin / wooden / simple / numb / one of the eight categories of ancient musical instruments 八音[ba1 yin1]
木
=
八
+
十
:
Mnemonic symbol: a Christmas tree. Malte Monkey is putting up a Christmas tree (木) in the bathroom of the space station (Ø4). He's using a cross (十) as a base to put the tree on, and decorates the tree with eight-balls (八).