Our introduction process was long. My girlfriend and I are both in school, so we had only a few days to acclimate them to each other. It didn't go well. Hikaru would attack Lost, hissing and growling, at every chance. So we kept them in separate rooms for over a month. We did our homework and things with Lost and then slept with Hikaru. We finally started letting him out and just keeping him with us. After a few months, we could finally leave them home together.
It took about 6 months for Hikaru to play with Lost, and about 9 before she would let him cuddle close to her. She is still very independent, but they play every day and have a lot of fun (until she's done). Lost has always adored Hikaru, and he's very submissive and understanding with her. He was never deterred by her, although he was scared of her at first. We've moved into a tiny apartment and don't have a lot of extra room.
So, once they got acclimated to each other, they shared a litter box for about 6 months without any problem. We had them sharing one of the large Budda Domes. We had to buy a different type of litter for a short time, and she peed on the stairs of the box. This is a litter in the past she has used and been fine. But I thought, maybe she's gotten pickier. So we switched litter back, but she still peed on the stairs. She would go in to poop, though.
We ended up getting disposable boxes and putting them in our tiny bathroom. Hikaru claimed them as her own, and never had any issue with them. Having the litter box was just a temporary solution until I could get the Budda Dome super clean AND get a new litter box for her. We recently got the new litter box, but we had to put it next to the Budda Dome.
NOW, Hikaru will use the new box. And she'll go a day (sometimes 2) without any problem, then suddenly, she'll pee on the stairs of the Budda Dome. It's very frustrating, and she knows she isn't supposed to (when we come home, she'll act submissive - which is extremely rare for her), and seems to feel bad when she does it.
I don't know what else to do. It's getting expensive to clean the stairs every day, and it worries me for if we ever have to go on a long trip.
Hopefully someone can help us.