This is clearly a single ticket/PNR (otherwise the SN flight from MAN wouldn't have a NH flight No.) so there is no issue (unless you absolutely need to be in Japan the following day). If you misconnect at BRU SN will rebook you to fly to Japan the following day - either on NH232 the following day (if operated that day) or via FRA/MUC or any other LH group gateway. Depending on the reason for the delay of incoming flight you may even be able to collect EUR 600 as compensation for delay under EU Reg. 261/04. Go ahead and book!

If your luggage doesn't make it to Japan with you, go on a shopping spree for essential clothing and toiletries upon arrival and submit the receipts to SN for reimbursement later on.

Anyway, 1 hour is more than plenty of time to connect at BRU and for your luggage to be loaded on NH232; transferring at BRU is easy and doesn't take long so unless your inbound flight from MAN is seriously late, you will make it in time to the NH flight.