consecrate sacrificial vessels by smearing blood, rift
衅 centers on a ritual act of smearing blood to consecrate vessels, and by extension a rift or quarrel, likely from the idea of a blood sacrifice marking a serious breach.
衅 combines 血 (blood) and 半 (half), suggesting a ritual involving blood, possibly an animal sacrifice, to consecrate objects. The exact historical development is uncertain.
Blood 血 is half 半 of a ritual: smearing it on vessels to consecrate them. A rift can be seen as a bloody split.
For キン, imagine a kin (family) performing a blood ritual together: kin -> キン, and the blood consecrates their bond.