Villain (V1) was a 30-something Asian who was playing consistent with a loose-passive read before this hand.

1/3. V1 (a bit over 200) limps UTG. Hero (600) calls with 88 UTG+2. V2 (500) raises to 12 in MP. Ends up being three to the flop, surprisingly.

Flop is J52r. Checked around.
Turn is 8, putting two spades out there. V1 bets 15. Hero raises to 45. V2 calls. V1 calls.
River is non-spade A. V1 checks. Hero bets 100. V2 thinks and unhappily folds. V1 tank-calls.

V1 turns over JJ and says he was worried I had AA, which I believe based on his body language and his not raising.

V1 later got felted twice. First when AA all-in preflop lost to a set of kings. Next, when he got it all-in with KK and lost when AQ hit an ace on the river. With KK, he didn't insta-call a shove and said he had to call even though he was probably against aces. I expect to see him again.

My assessment of this player is that he is nervous about non-nut hands, but he won't fold even though he is sending out signals of weakness.

When I am at the table, I like to think through scenarios of possible future hands so that I take less time to act. Here are some scenarios I considered. V1 is sitting two seats to my right in all examples.

Scenario 1) Limped pot. Hero has 98o in the BB. Flop is QJT. Hero bets 2/3 pot on flop and is called. Turn is a 2. Hero bets 2/3 pot and is called. River is a 7, no flush possible. Hero bets whatever amount and is raised. Should I fold to a min-raise? Should I ever call to a raise larger than the minimum?

Scenario 2) Limped pot. Hero raises on the button with Ax. Villain is one of two callers. Flop is AJ2. Check to hero who bets 2/3 pot and is called. Turn is 7. Checked to hero who bets 2/3 pot. Villain calls. Other caller folds. River is 9. Villain checks. For what values of X should hero value-bet the river?

Scenario 3) Straddled pot. Hero is in BB. Five limpers. Villain is short-stacked and shoves for $87 OTB. What hands should hero be playing in this spot?

Scenario 4) Villain open-limps. Hero raises with AK. Heads-up pot. Flop is 872 with two spades. Hero c-bets. Villain check-calls. Are there any cards that are not A, K, or spade that hero should fire again on the turn if villain checks? Should hero consider a thin value bet unimproved since he might be against a straight or flush draw and have the best hand?

1) fold
2) check with all kickers
3) KK+
4) I would bet all turns here, but primarily as a bluff. In the hands you shared, I don't see any real basis for your read that he's reluctant to fold weak hands. He shows up with monster hands and thinks about folding them. The fact that he can't find a fold with the third nuts doesn't mean he's going to be happy to call bets with weak one-pair hands.

My read isn't that he's reluctant to fold weak hands, it's that he's often quite strong when he sincerely acts like he is weak, so you can't eliminate as many good hands from his range.

Hand 1 is a bet/fold. He's only raising with the nuts yet you can get value from two pair type hands.

Hand 2 hard to say if we should bet as we don't have much an idea of how wide v will limp/call pre. Generally though I'm value betting two pair and AQ/AK/AT & A8. We chop/value own ourselves with any Ax that's worse.

Hand 3 QQ+, AK dude open-limped JJ at a 1/3 game. He's gotta be pretty narrow here.

Hand 4 we should be barreling any card 9+ because we have oodles of equity but we should not value bet the river as we won't get called by worse.

Agreed, but it's important to keep the pressure up on these kind of players when they're not showing strength. He mathematically has to fold a lot if he's limping a bunch of hands and isn't comfortable playing marginal hands.

Scenario 1: Given villain description, I probably make the tight fold even to a min raise. Villains that tight about raising river always have a straight here, so you are either chopping or losing. With a good feel for his range and how likely he is to have AK/K9 I may call.

Scenario 2: Probably check unless he limped in LP or a blind. In those case I may bet AQ/AK. Once I get a better feel for how weak of aces he will limp/call preflop and station off post I may go wider.

Scenario 3: Shoving range is likely to be different then his normal playing range and I would need a separate read on it. Absent any other information, I expect very tight. I might even fold AK here, only playing QQ+.

Scenario 4: Probably not, but depends on villain's limp/call range, what he will chase with and how much he will give up to a 2nd barrel. If he is tight/passive and stationary he wont' have many draws because you block the big flush draws and he won't give up his single pairs much.

How loose is this villain and what are the effective stacks? In your examples, he showed JJ, KK, and AA. Is he more tight-passive? In general, he sounds like scared money and I would fold almost all non-nut hands when he raises. How weak will he check-call all the way to the river? I think figuring out the answer to that question will answer most of your scenarios.

#1: Fold. There's almost no chance he's bluffing after you bet 3 times after the flop.

#2: Value bet all two pairs and AQ+. I'd check the rest

#3: KK+, maybe QQ+/AKs. With 5 called $6 straddles, hero needs about 41%. He sounds like he only gets it in with monsters. Short stacked he'd probably add QQ and AK to his shoving range.

#4: I'd probably check since I don't have any fold equity. I'd bet if villain has a decent size stack and I think I'll get paid big on the river if I hit.