ulterior motive; secret scheme; plot
Refers to a hidden plan or calculation behind someone's actions, often with a negative or suspicious tone. Common in expressions like 魂胆を見抜く (see through someone's scheme).
There must be some ulterior motive behind his kindness.
I saw through the other person's scheme and skillfully dodged it.
complicated circumstances; intricacies
A less common, somewhat literary use referring to the complex inner workings or hidden details of a situation. Often appears in explanatory or narrative contexts.
It took time to unravel the complicated circumstances of the incident.
I saw through the ulterior motive behind his kind words.
There must be some hidden agenda behind him suddenly being so kind.
She smiled while concealing her true motive.