The reason why Germany is that harsh in Hetalia is because the place in time.
When Prussia died, Germany became softer, Smiles more often and starts living without militaristic influence.
He got terribly depressed and lost self-consciousness as soon as he heard that his brother died.
He eventually overcame it and quite lives with Northern Italy.
Those two spend a lot of time together.
Italy helps Germany being not so strict and keep him happy, and Germany teaches Italy how to bake, how to take care of animals.
They also improve Germany's sleep counting qualities.
Germany, now a days changed his style almost complete. He still is into that military stuff but way more relaxed.
He lets his hair fall normal and it is a little longer than usual.
He mostly wears at home comfortable clothing like a oversized Shirt with Jogging trousers (?).
He also came to the though that his body stature is one of many reasons why people are afraid of him.
He stopped training his muscles, yet still he trains to stay fit. Like running a few laps and some Yoga something like that.
He is quite thinner now a days and smiles and speaks often.
He improved his English and his accent isn't that hearable anymore.
He managed to get along with Poland, France, Britain, USA and several other countries.
He also offered social help to me (Japan). But I declined. I am not that socially awkward.
One in one, he is quite a complete different person now a days and the only reason he is presented in Hetalia like he is is because the time.
Bonus Headcanon; Prussia died peacefully but Germany couldn't say goodbye to him because Prussia died while still living with Russia.