Upvote:1
If your items are new or appear to be new, it would be best to register them with US Customs before departing the USA to avoid duty hassles on the way back. The items you plan to leave, should also be registered in case you can not leave them in Japan, but I would do a separate registration for them to avoid the "where is such & such" questions when you return.
As carry on items, they are subject to TSA's OK. If anything looks like a weapon or potential hazard, it might be good to contact a TSA supervisor at the airport ahead of time to make sure they won't stop you at the last moment.
Entering Japan you will want to declare them if they represent higher value. The items you plan to leave behind will likely be subject to duty, so bring copies of the receipts for those items purchase or if they are things your company manufacturers, then some documentation of their market value.