I'm not going to join this jam if the theme is tranquility or anything that forces me to make a casual game. Casual games are not my cup of tea, thank you.
The theme is not forced at all. And its open to interpretation, tranquility for someone may mean a bloodbath of bunnies.
I can totally see that. "Time for a nice, relaxing sunbath on my lawn--what?! Why are there so many bunnies here threatening to ruin my peace? The only way I'll get any (*achem*) tranquility around here is to kill all those damn rabbits!"

So, where's that Valhalla fella with the next letter? The way I see it, if there's a different letter where the q should be, then its not tranquility. If the letter is in a different spot, and still fits with tranquility, then I'm thinking it is tranquility. Does that make sense or does sense make that none??
Heehee.
Until then though - I think we can safely assume that it's eja_u_a_ion... Sorry - that word just caught me by surprise when I was compiling my list. 
Wow. That would certainly make for some interesting (and completely inappropriate) games. I don't think that's it, though...just a gut feeling

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I love how many people have at least subconsciously latched onto the idea that the theme is tranquility. I, for one, welcome our presumptuous overlords

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-IMP