It's probably even more important in canon, although whatever magical talent the Ryudo family had (they had to have had some, as they knowingly founded the temple on a leyline) has dwindled down into just a slightly higher spiritual awareness than most people. Still, upholding the family tradition definitely comes up a lot in canon.

If Issei was really set against being a monk, he could probably get Reikan-nii to inherit. I think most of what he does is a genuine desire to focus on being a monk. (For one thing, he's really bad at lying or just not being up-front with anything, so pretty much everything he does is genuine.) ...He's going to freak out when he realizes he himself needs a heir, though. Thank you for reminding me to mention that some day.

I'll keep those places in mind! Thanks once again, you're a great help.