In Japanese each letter represents a syllable rather than a vowel or consonant. So you don't get words that end with consonant sounds (other than "n", which is treated as a syllable on its own) in Japanese. Foreign words and names have to be adapted to fit this scheme.
I'm not sure on the context of "dosa". If it's in the context I'm imagining of "how about this?" there's a lot of modifications you can use at the end of a sentence instead of sa for different emphasis.
Japanese writing and how things are pronounced are a little different. Phonemes ending with an "u" sound are by convention often the place holder for an unvocalized sound. Think a syllable boundary between two consonants in English. "Batman" would be written "Ba-tu-ma-n" in Japanese but still
pronounced "Batman". For example in Paranoia Agent, the villain is always stated as "Shonen
Bat",
not "Shonen
Batu", but the word "bat" here would in fact be written with the syllables "Ba" and "tu". Say "BAT" in English and notice that no matter what you do there's a slight hiss of air after the final "T".
That slight exhalation of air is what the "u" in Japanese "tu" actually signifies. English also has that sound, we just don't write it down so we forget it exists.
Some other examples are:
- Desu, is almost always "des". And the question-end "desu ka" is more like "deska?" rather than "de-suuu-ka?" Actually in anime, characters who put an emphasis on the final "uuu" as in "des
uuu" are almost without exceptions ditzy heroines in comedy anime (very prevalent in 1990s and early 2000s harem comedies). One example is Steel Angel Kurumi. Pronouncing every syllable of "desu" is a standard anime trope signifying an airheaded girl.
- Also,names, Natsuki and Satsuki are always pronounced "Natski and Satski"
never "Nat-suu-ki" or "Sat-suu-ki". In any event, the middle "u" sound is as shortened as you can make it. It's the same in "suki" or "daisuki, the "u" is shortened to the point it's basically just an exhalation of breath in between the other sounds.
Another example is Kill La Kill. Senketsu and Junketsu are always pronounced "Senkets" and "Junkets". There's basically no sign of the "uuu" at all.