Adding two also circumstantial things that might swim in similar waters:
- According to Touka, there is someone else with conditions similar to Yasu's that got admitted to the hospital a lot earlier than her. If this person indeed showed divine symptoms and indeed also was Rin's bio-mom (considering how she was found and handled, this would be a likely result for her), then this strengthens Rin's tie to Nozomu. Granted, this person could be Kaori for all we know, someone whose past medical history is more documented in the game than the rest of the characters.
- There is, however, canonically one person who did have divine symptoms and did have sex with Nozumu at the same time;
Sekai. If one plots a regression line and correlates seeing things, hearing things, and being clinically insane with sleeping with Nozomu, then it strengthens ties of both Rin and Sana to Nozomu.
---Counterpoint Section---
- The statement "being fucked by Nozomu leads to experiencing supernatural things" is not impeccable. The causality between the two may not exist and might not be easy to prove. Sara and Sekai's experience might have started
before they slept with the culprit in question. Yasu, on the other hand, has no problem being a cute little crazy person without anyone fucking her or her mom (as far as we know).
- The root of the whole "Nozomu Arakawa being the dad of Rin and Sana" business is the fact that both moms experienced the unexplainable while one of them is sure to linked to the first god with the name
Nozomu. Because of that, the older Arakawa brother automatically bears the blame of impregnating girls and
fucking them crazy despite the fact that we know very, very little of him (but to be honest, why would you think otherwise?).
However, to disengage god's doings from older Arakawa's alleged doings, I once proposed the idea of human Nozomu being named after the god Nozomu for folks who find Sara and Rin's bio-mom's connections to the first god non-negligible, but find the idea of Akira's brother possibly being the dude quite far-fetched. This is an intentional exploit of Saki's religious nature but no further details of what religion that was. This way, Sara/Sana and Rin keep their connections to the first god but Nozomu Arakawa the human has nothing to do with it. We thus don't need to force the blame onto him when we again, know very little about him, even if his suspicion level is, objectively speaking, through the roof.
- Following a similar track to the bullet point above, Sara's and Rin's bio-mom's connections could potentially be "established by submitting yourself to Pegasus" on a casual walk on your way home. This takes "having sex with the older Arakawa brother" completely out of the equation if you're willing to believe that Sara and Rin's bio-mom might have simply been favored by entities or messengers/embodiments of some gods out of nowhere.
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All of the counterpoints above do not reject the fact that Sana and Rin might be related via something, blood or no blood. I am merely exploring the possibility of "maybe it's not via Nozomu Arakawa".
- Last and definitely the least: if Nozomu Arakawa indeed is the bio-dad of both Sana and Rin, this game would have way too many fucking nieces and way too many niece fucking. I think I can accept one of them being the hidden niece and it would be a proper shocking reveal. If both of them are nieces then shocking turns to comical; like a "why stop at 2 (or 3) nieces when you can have 20?" thing.