As someone who's been using Tenso for 3 years now, don't worry
This is to comply with laws that were passed about 2 years ago in Japan that require this sort of information for middleman services (it's to make sure we're not resellers selling things illegally in our countries, basically). Tenso do need this info because of how they operate - no one is going to steal your identity, promise. At least no one's stolen mine yet lol