Cat probably stopped them, like he's been implied to have done all the time according to the last omake/extra. He is very vigilant to keep them from 'attacking' each other, supposedly. He thinks they don't like each other, and wants to keep the peace. I also still think there's an issue with the elixir that'd make it a bad idea, too, but Hata may not have thought of it, so maybe it isn't really a problem.
Anyway, Chapter title seems to say "I tend to buy souvenirs" when I use the Lens translate thingy. The text on the left side of the splash art reads "Off-shot from a date in Harajuku", and the text at the bottom of the shirt says "Tonikaku is cool"