When Roland/Isono finally gets married he of course invites the Kaiba brothers. Seto is a little reluctant to go, after all, business and private should be kept apart. Plus, public displays of affection and all that jazz. But Mokuba eventually convinces him they should go, which brings up the question of what to buy for him.
Not a big issue to Mokuba, who knows how to socialise and what is on their wishlist. For Seto, it takes a little more effort.
In between, he overhears against his will, that he and his wife-to-be are expecting a child, although they are not very far along yet. Nothing Seto quite considers his business, but still can’t help remember.
When Seto eventually appears—still shocking and deeply touching Isono—he is holding a relatively small present.
Not expecting much, he opens the present first regardless, and finds what seems to be only a short letter at first. For a second he believes it to be a note letting him know Kaiba Corp is letting him go.
Instead, he finds out that Seto opened a bank account for their future child—and all coming children they might possibly have—with a generous starting amount he will add to over the years, assured that only their children will have access to it for whatever they need it for. May it be a good school/university or a home. This is followed by a short, but (for Kaiba levels) personal note promising to make sure his family is protected just like isono made sure to protect him and Mokuba for years.
While most people consider it a nice, but not too big gesture, considering he is Kaiba, Isono, knowing the full history of the Kaiba brothers, what happened to them, what their own family did to them, is deeply moved to know that Seto’s first instinct was to protect the children from the same harm done to him, should tragedy strike.
Once the child is born Isono for once breaks the rule of keeping work and private life separate, to ask Seto if he wants to be the godfather.
Seto is more touched than he would ever let on, but just as worried that should it come down to it, he would fail the job.