Yeah, I saw the "loan basis" line and it appears to be a funky translation. You don't actually need a credit card in order to buy/activate it, and they never mention returning it when you're done. I think they just mean that if you, say, put 5000 yen in recharges on it and then damage/lose the SIM you can keep the service intact and reduce your losses by paying the replacement SIM fee instead of buying the whole thing over again. That's the only way it makes sense.
This is great, and much more cheap than B-Mobile. People need to be really aware of this though:
And 2,838 yen to recharge 1GB/60 days
Is it? I can't see any price on the website?
Edit: I found the price. It's 3000 JPY for the 100MB package and 5000 JPY for the 500 MB package: