Not about the body he gives but I'm talking of the fact that in Septem's route he can give you a gift one similar to nulla's if you don't cross his boundaries too much (and act too much like Father), plus it does have a scene if you interact with it unlike nulla's which does nothing if you click on it (Also don't go into nulla's route if you have septem's gift, he WILL notice and give you a nasty stare 💔)
Which one are you referring about, meeting Father or getting Septem's gift?
To meet Father you need to be on septem's route, when you and him are in the garden of his domain, a white spider will appear on your screen, click on it and continue on. (You also can meet him during Nulla's memory route)
For Septem's gift, he only gives it to you if you have high affection with him, in order to get it you must not cross his boundaries or upset him too much, some of these include not eavesdropping on him praying to father, not choosing the option to insist right after the scene where he checks on rafael, prevent him from hurting one of the council during the meeting, and I think that's pretty much it. I recommend not skipping too much since you could miss the spider appearing or obtaining the gift which require you to read through the scene.