Daito-ryu does involve some practice at giving and receiving various atemi on a human body.
But I must agree with the others that the Russian martial art of Systema probably is closest to what you appear to be looking for.
They've got some very very unorthodox ways of hitting. I've experienced practitioners who can cause you to collapse in the strangest ways through different strikes.
They also teach how to breathe so that pain can't enter; they dish out strikes with whips and wooden sticks and you learn to absorb it.
Where in S.A. are you located? I might be able to point you to someone there if you're interested.
By the way, if you want an interesting discussion of atemi as it relates to Aikido, there are some thought-proving essays in Ellis Amdur's "Dueling with O-sensei."