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Get good scrub. Eventually you will win. 

A good deck for beginners might be a Hololive deck using the Marine level 3 climax combo any level 1 climax combo (I recommend Korone or Pekora).  In most decks you'll want between 16 and 22 level 0 characters.  Make sure to run 4 copies of a character with the Brainstorm ability or similar to replenish your hand by spending stock.  It's also important to have a card with the potential to add climaxes to your hand either by drawing cards or exchanging one climax for another so you can use your level 1 climax combo as many times as possible.  For most decks, level 2 characters aren't super useful, so unless you're playing with a specific strategy in mind, I don't recommend using more than 4 level 2 characters (not including backup).  I generally play with 8-10 level 3 characters, and the rest are level 1.   Try to keep your deck to 1 or 2 colors (not counting level 0 characters) as more colors means you'll be more likely to be locked out of playing certain characters.  Almost all decks play a level 3 climax combo that deals damage as a "finisher", you'll want to run 4 copies of whatever finisher you choose.  Don't try to play standby as your first deck (the red trigger icon climax that looks like a power symbol). 

As for how to win, it's important to pay attention to where your and your opponent's climaxes are.  If your opponent doesn't have a lot of climax left in deck that's a good time to play a climax for extra soul.  If you have climaxes in your stock or multiple in your hand, try to get them into the waiting room before you refresh.  When most of your climax are in waiting room, but you still have a lot of cards in deck, you need to do everything you can to mill your deck or refresh with an ability or you're in for a world of hurt.  Stock is a very important resource, so don't use "Encore 3" unless you absolutely need to, and never use it on your own turn.  If you know your opponent has too many climax in deck for you to deal damage, there are certain abilities to deal with that, these include the infamous stock swap ability or cards that do something when damage is canceled.

As for beating the computer, the Persona AI should be the easiest since it's an old deck and the AI hasn't been updated in years.  Axis Church is a weird deck that's designed to be annoying and most people don't play like that.  The Emilia AI is probably the most normal and least aggressive deck, but it's also the best at managing its climaxes.  Its weakness is that it's not good at beating characters with 8500 or more power before level 2, it's also weak to backup cards with the ability to remove characters whose level is greater than your opponent's level.  To avoid the soul reduction effect the turn after they've played their level 3 climax combo, you can use a card with an ability that "flickers" (puts the opponent's character into memory then returns it), or downgrades (forces the opponent to exchange their character with a weaker one in their waiting room).  The Mushoku AI is using a deck that's actually quite overpowered.  A good way to beat it is using cards that kill characters whose level is greater than your opponent's level or specifically kill level 1 characters.  Also if you go first it will almost always kill your character using Rudeus unless you have an extra character.  I'm not sure what to say about Shion Aqua deck, sometimes it has 1000 IQ moves, sometimes it just throws away the cards it needs.