How I became Bankrupt

A businessman, trying to extract the business plans of his biggest rival, falls in love with his son.

Basically,
Levi Ackerman and Erwin Smith are trying to get rid of their competition from the market - the long-time number one - Grisha Jaeger.
They devise a plan in which Levi writes to Eren, Grisha's son, as an anonymous student from his University trying to befriend him.
However, the plan becomes complicated when Levi begins to care about Eren.