Super no Ura de Yani Suu Futari

Both of these shows feature a vibes-based romance in the city night. YaniSuu is much more slice of life, while Call of the Night has a vampire action dynamic. I would be hard pressed to find another show that pairs as nicely with either of these. 

Short anime series revolving around 2 people discussing their daily life around a specific location, namely at a food court and at the back of a supermarket. 

Both anime feature a female protagonist with a beautiful, unusual voice who loves to tease the male protagonist. Both have a very good and frequent soundtrack throughout the episodes. Note: Nazo no Kanojo X is also known as the "saliva anime," so only watch it if you don't have a problem with that. 

If you liked Smoking Behind the Supermarket with You, you should give I Made Friends with the Second Prettiest Girl in My Class a try. I think the two have a similar vibe in the way the relationships develop. Maki and Umi spend a lot of time together just talking, watching movies, playing games, eating together, etc. There's no need for constant misunderstandings or pointless drama to keep them apart. I also really liked how natural their chemistry felt. Their relationship slowly develops from simply enjoying each other's company, and they actually communicate when something is bothering them. It's obviously a different kind of story, but if you liked the relaxed atmosphere and everyday relationship in Smoking Behind the Supermarket with You, I think this one is worth checking out. read more 

Both MCs are overworked salary men who find comfort in being around the female MC of their series. Both MCs also have a deep admiration for their female counterparts as they bring them a sense of reprieve to their menial lives. Not to mention both series are WHOLESOME AS CAN BE!!! 

in both younger girl is flirting and trying to date an old guy who plays 'shy' 

These are both chill anime vibes with low-key vibes that carry it. Both are lighter watches (pun intended) and feature a similar style of female MC and also smoking if I remember correctly for Kowloon. 

Basically the same anime. Just that one is with schoolkids and the other with working adults. You might even call this Karakai Jouzu no Yamada-san...