Make a series of random tables based on 1: Terrain, 2: World themes, and 3: PC motivations.
First things first, you'll want to identify: What do you want to achieve with these encounters? From your post, I believe that your priorities are:
1: They should be random (I assume, so that you don't have to plan out the whole world)
2: They should be relevant to revealing the world - not just some random violence
3: They should be relevant to the character motivations.
To that end, now you start to make your random tables.
The first set of tables will involve the descriptors for the hex itself. You want to identify the types of terrain. As you have described this as Post-apocalyptic Tokyo, so you won't have the normal 'forest, mountain,' etc terrain. You will have 'High-tech city' 'steampunk' 'slums' 'destroyed city' 'returned to nature' (with plants growing over destroyed buildings) 'laboratory complex'.
Perhaps you have different communities within PA Tokyo, so you'll have that as a descriptor, too. This hex is controlled by the Blue Thunder Megacorp. This hex is controlled by the Free Republic of Tokyo. This hex is controlled by the NeoEmperor. This hex is controlled by the local warlord / gang.
Finally, some hexes might have special modifiers. This one might have high radiation levels. That one might have crystals growing everywhere from an escaped experiment. etc.
Once you have your list of 'hex types' and different modifiers, now you make your second set of lists - and for these, you need to decide, what do you want to show about the world around them? What do you want them to discover about your world? Such things might be:
1: The NeoEmperor seems harsh and violent, but he is just trying to protect his people from a violent world.
2: The common people are trapped in power struggles between the various powers.
3: Blue Thunder Megacorp is doing genetic experimentation on the homeless.
4: The Free Republic of Tokyo is secretly controlled by a council of escaped lab experiments
5: The FRT council are actually all telepaths, using their powers to control the populace.
etc, etc, etc. Decide on the motivations of the players in your world. Say you get a list of 20 of these 'story themes' in your world, you can roll a d20 and pick a story theme to try out.
So you've got a list of random hexes, and a list of random themes. One more randomizer is needed: Your players' motivations.
Work with your players to generate a list of motivations. Say ... 3 for each player. So one player has as his backstory that some corporation ruined his family and left them homeless in a radioactive part of the city. As his list: "get back at the Blue Thunder Megacorp," "Make lots of money (for my family)", and "protect others from being taken advantage of."
Now you have your tables. How do you use them?
Well, start off rolling the terrain. This one is ... (roll) A high-tech city, controlled by (roll) the Free Republic of Tokyo, and as its special descriptor, it is (roll) actually pretty normal. So you know by this that there is a telepathic field dampening people's free will. The people here all seem lifeless and uninspired, like cogs. You also know that the players need to make a will save (or whatever the equivalent is in your system) or start taking negatives to any violent or high-energy actions. It is full of bright lights and efficient machinery, but none of the neon lights and night clubs you'd expect from, say, a Blue Thunder controlled high-tech city.
Now you roll on the themes. You roll 5: The FRT council are actually all telepaths, using their powers to control the populace. So you want to highlight exactly how strange the citizen's actions are. How? Well, roll your 'player motivation' random table. You get 9: "Jane: Spread the word of my religion, (based on pre-apocalypse taco bell commercials)"
All right. Now you use your imagination. If you want a more active conflict, do this:
So as they're walking along, they see a fleet of white vans go past. No one looks at the white vans. It's like they're not even there. They stop up ahead, and everyone completely ignores it as a squad of white-powersuited military types go rushing into a store and there's a lot of noise. Then, the white-powersuited soliders start dragging people wearing high-tech headbands out of the building, and tearing the headbands off. The people scream, go wide-eyed ... and then suddenly go peaceful, and wander out to join the rest of the crowd as if nothing had happened at all. And Jane notices that one of those people had a handful of papers, and when the headband gets torn off, she drops them, scattering "Church of Yo Quiero" pamphlets everywhere.
Or, if you want something less active and more passive, then the player is trying to pass out Church of Yo Quiero pamphlets, and getting ... far less response than usual. People aren't listening ... they're not even annoyed. They just look and shrug and move on... and if Jane starts getting more fervent, suddenly they pay less attention to her. It's like she's suddenly unseen and unheard. She can't get ANYONE to respond to her, as the ruling council telepathically deletes her from the populace's perception until they can either overcome her mental defenses or she calms down enough to no longer be making a fuss..
I hope you get the idea! Keep your random tables general and focused on your goals, then combine the elements they bring up into a quick little story or scene that follows those prompts to make the scene you want.