aight so we're left with the following:
2L (Himari)
1L 1D (Arisu)
1L (Corpsey boi)
1L 1D (Kitou)
Himari is literally 100% going to die at this point, she has no Death cards to live the final selection. Trying to survive at this point just ensures she dies and Kitou wins. She and Arisu Life each other, then she gives her phone to him. He Deaths Kitou's phone because that's the one with the Death card on it (thanks for that info, Kitou). That removes Kitou's ability to use his "Death" card in the final round, as Kitou's phone will not acquire a "Life" card to be considered active for the next round. We end up in the final setting with:
1L (Himari's phone in Arisu's possession)
All other cards are spent or inactive, so Arisu just wins by default. He can Life his own phone, even though it has no cards. He spent all his cards and wins according to the rules.
Can't wait to see what other games we'll get with nice puzzles like this. Trying to "solve" the game before the story reveals how it plays out was one of my favorite things about this series.
(Plot predictions unrelated to the game's mechanics: doesn't matter if Arisu realizes this strategy, he won't want to employ it - Himari will end up self-sacrificing like a lot of the characters in the previous story, author really likes having very generous characters juxtaposed with or taken advantage by cunning and ruthless characters, but there's a lot of themes of humanity helping overcome and triumph too)