The only time I ever pick up Keroro is for his photo shoots
And that's once a week for maybe 10 minutes at the most. He jumps and struggles so much I'm just afraid of accidentally injuring him, so I do it as little as possible.
If I handle him more are you saying it'll desensitize him to it? Because everything I've read says to handle them very little (fragile skin, etc). But hey, I'm open to trying something new if it's safe. Not expecting him to get puppydog-friendly of course lol

Just a side-note, he isn't aggressive at all just skittish.

@Tim,
I really like the bathtub idea. I bet he would enjoy it too. I do it for my snake, so I could make a day of it.