'become each' is not a grammatical phrase in English.
You could write something like 'become one' or 'become unified.' For example: The two companies decided to become one in order to maximize profits.
Now they have become each other's enablers.
"They could each become each other".
They have become each other's biggest fan.
The two countries have, arguably, become each other's biggest long-term threat.
OZ: We're also looking for some kind of normalcy, but we have become each other's abnormalcy, I'm afraid.
Before 1914 Germany and Britain had become each other's largest trading partners.But the forces for war proved stronger.
They became each other's support network.
"Like Dickens, Tolstoy became each and every character he wrote.
Ms. Sarukkai became each woman, reacting to Krishna differently.
We learned how to cope with each other's personalities and moods and became each other's motivator.
Through childhood and adolescence, Andy and I became each other's best companions, roaming bush trails together in the Eastern Cape of South Africa.
