FWIW, I think Nishio's atemi (as demonstrated in the Yusuru Budo book and DVD series) is rubbish... and if I were to be more polite - at best, pre-school level atemi waza.
The videos posted by Salim are closer to what I learnt in karate-jutsu and jujitsu, and I think are far more appropriate in terms of setup, execution and follow thru for Aikido 'techniques"... and closer to what I've seen of good hapkido.
I would suggest to the OP, get yourself an anatomy reference and a good set of pressure point charts. Find a list of various hand/fist formations and kicking techniques used in karate (or even CMA in general). And then find yourself a teacher who can teach/show you this stuff - and then work out how you can integrate it into your Aikido "techniques".
"Pre-School" Atemi Waza??? LOL
Well everyone is entitled to their opinion even if it's based on reading books and watching videos and not actual experience.