I’ve been playing the game in offline co-op. If I play a section by myself, will the second character lose inventory when a human player takes over again?
No. It will just revert back to your big “inventory space” when a human player joins. The next time you play by yourself, the other character’s inventory will be empty, but all of his/her stuff will be in your main inventory space.
So, if I play by myself now, I will get all the stuff Shiva has.
When the human player re-joins me, they start from scratch?
If ‘start from scratch’ means what I think you mean, then no. Each individual human RE5 player has 3 inventories, really, a long term inventory and then short term inventories for Chris and Sheva. Depending upon how you start the game and with whom the game will sometimes effectively clear out the short term inventory of Chris and/or Sheva but once you aquire an item you’ll never lose it unless you use it (if it is a one-off like grenade), sell it, give it to another human player or discard it (or your save game gets corrupted – motherfuckers at Capcom, I will NEVER forget!!!) If it doesn’t show up in the short term inventory of the character that last used it, it’ll be in your long term inventory.
Each human has their own individual long term inventory and can equip their own character only from their own long term inventory even if they are playing co-op with you. That’s why the game will clear out a character’s short term inventory if you suddenly start playing co-op with a new player. The co-op player you’re playing with can’t use the items in your long term inventory unless you give the items to them specifically (and not all items can be given) because long-term all items are tied to YOU, not Chris or Sheva of your game.
You should really play around with the inventory system to get a sense of how it works since it is a very important part of the whole meta-game of RE5, but just to give you the peace of mind to do that, I’ll tell you that the inventory system is very reasonable and you aren’t going to get into a situation where playing a certain game type has unintended consequences that wreck your inventory. The only thing you need to keep in mind is that the long term inventory is tied to you as a person and not any of your characters (their inventories are very transitory and managed by you at game start, between chapters and after dying), so don’t start a new game, give your characters some weapons out of your long term inventory and then discard them in that game assuming you’ll still have them saved in some other game save, because you won’t, you’ll be discarding them from your long term inventory as well. That’s the only inventory system misconception that could really get you in trouble.