That sudden shift from grumpy to cuddly sounds like such a sweet surprise! Sometimes older cats just need the right little spark to bring out their softer side, and it sounds like Luna’s playful energy might be exactly that for Miso. I had a similar experience where my usually standoffish cat started grooming a new kitten after just a few days - it was like he suddenly remembered how to be a big brother. Keeping an eye on their interactions without hovering too much is key, I found. Letting Miso have his own quiet spaces to retreat to when he needs a break helped keep things balanced. It’s great you’re doing supervised visits; maybe just keep offering those calm, positive moments and let them set the pace. Your gentle approach is probably what’s making this adorable friendship blossom so quickly!