I have a 10 month-old neutered Ragdoll male who is a very friendly, lovely cat. He's an indoor cat and has been from day one. We work full time, which means he spends a large portion of the day alone. He has a lot of energy when we get home and loves to play. With him being so sociable, we could tell towards the end of the working week that he was getting a bit frustrated so we knew he needed company when we were out. Naturally we decided to get a second cat. We had initially planned on getting one younger or a similar age as we're aware kittens have a lot more energy than adult cats. However, my partner's cousin was looking to rehome her 5-year-old spayed female British Shorthair. She's also an indoor cat and has been a single pet for 5 years. We knew there was a chance it wouldn't work due to her being an adult cat that's used to her own company. But with them having a similar temperament and her being quite playful herself, we decided to at least give it a go and have also arranged a fab permanent back-up home for her just in case it doesn't work (my parents who have no other pets). We did all the recommended steps to introduce them - Feliway plug ins, kept them separate whilst swapping scents, let them explore the other's space without meeting and put the feeding bowls on opposite sites of the door. They were pretty comfortable around each other's scents to we let them see each other through a barrier. On day two of using a barrier the kitten actually leapt over it and they met properly much sooner then we had planned (she'd been with us less than a week at this point). To our surprise they just sniffed each other and started playing! We've had the new female cat for about 3 weeks now and up until about 4 days ago they've been brilliant. They chase each other, play and sleep next to each other. Now, something's changed... The new female cat has been hissing, growling and using claws when they play fight. At first we thought it was the kitten getting too carried away and annoying her (I should point out that he's a big kitten and is actually the same size as her right now). But when they're 'fighting' he's making no noise, his ears are upright and he doesn't seem to have his claws out. It's like she thinks she has to defend herself when he comes over to play and is getting quite aggressive (and very vocal) with him. He's not got any injuries from it though. Putting it down to the kitten simply wanting to play more than her, we've been trying to help burn some of his energy through solo playtime. But he's just lost all interest in playing with us and his toys, which isn't like him at all. He still tries to initiate play with the female cat, then after a few minutes of mutual play she'll start hissing and growling at him. Once that happens he wonders off and then we'll hear him meowing from another room. We grab some toys and go find him, but he just won't play (we've tried teasers, a laser, ping pong balls, flashing balls, catnip on his toys etc) - no reaction from him at all. Normally when we pick up a toy he goes nuts, so I'm getting a bit concerned. From the way they've been sleeping next to each other and don't go out of their way to avoid each other, it genuinely seemed like they're getting along. But then surely losing all interest in playing with us/his toys isn't normal for a 10-month old kitten who would usually chase a ping pong ball for thirty minutes straight? Could I be reading the situation wrong? Just incase anyone is wondering, there's been no inappropriate furniture scratching or toileting problems with either cat. The kitten hasn't lost any of his favourite napping spots since she arrived and they have separate litter boxes and feeding/drinking bowls. Sorry for the essay, I could just be worried over nothing but any advice would be amazing. Thanks!