Yes, you want to remove that shoot as it emerges from the trunk. This tree is grafted and that is the understock that is growing. Not removing it will allow it to dominate to the point the desirable topgrowth will be overwhelmed and eventually fail. Other than that, no pruning is necessary at this time - JM's do not require much at any time :-)

btw, this forum is intended more for design discussions re: Japanese gardens rather than issues with individual plants and is not very heavily trafficked......like not at all!! You will get much faster and more thorough responses posting your questions on the Maples forum - JM's comprise the bulk of the discussions there!

Thank you so much for your help...and your quick response. I will make sure to post any future inquiries to the Maple forum. Thank you for that suggestion.