I really liked this drama, and I give it a solid 8.5/10. Somewhat high cheese, predictable and doesn't ask much of viewers, but great chemistry, skinship, emotions, and fun makes it a solid watch.

What I loved:
• The development of the characters, especially Sumire. It does a great job of showing how lonely and tightly wound she is, and why exactly her relationship with Momo not only works but is super crucial to her emotional health. I love the way it shows in the small sometimes subtle changes in her behavior and comfort around not just Momo, but her friends, coworkers, and even Hasumi.
• Momo's development was great as well, if not somewhat secondary to Sumire's. While he is very child-ish through most of the series, it’s not to the point of being totally grating, and we do get to see him mature a little towards the end. Also his unwavering dedication to Sumire is just damn precious.
• Overall mood is great - it remains upbeat and easy to digest without being too absurd (a feat considering the premise) but doesn't skimp on the emotion. It's still deeply heartfelt, but fun and funny at the same.
• More skinship and sensuality than most Asian drama’s I’ve seen, which is totally welcome in my book. The series treats sex as totally normal, relatable, and even humorous but without ridiculing it. The sexual tension between the mains makes their developing relationship that much more fun to watch, while the lack of chemistry with other characters does a great job adding to the overall theme of their relationships.
• Sumire's wardrobe is goals.

What I didn't like:
• Most of the secondary characters and sub-plots I really couldn’t care less about. Yuri and Ran are adorable, but Yuri’s sudden marital issues were out of left field, felt pointless, and a little sexist (why did Yuri feel she needed to change?). Fukashima was a total fail redemption-arc for me and was never likable or empathetic. I couldn’t buy her relationship with a certain someone at the end, either. Sumire’s sister was a wasted opportunity, but her purpose was served at least.
• The “pet” thing at times got a little cringe, for me. I don’t like too much cheese in my entertainment and Kimi wa Petto danced on the edge of my comfort zone a few times. Thankfully there wasn’t too much of this, despite that being the core of the plot. But when it did get to higher levels of absurd I admit I fast forwarded through some of those scenes.

Overall it’s a very pleasant romp of a drama, especially if you need something uplifting after a particularly heavy show.