In kata, why does uchidachi start to strike?
Just to let shidachi practice the physical movement of oji waza?
I think it should not be that simple. Otherwise, it would be trivial to practice kata.
As far as I learned until now, an attack should be initiated from seeing, or by making an opening.
In kata, it seems like uchidachi is going in for attack blindly just because the distance is reachable.
Kata 1, issoku-itto-no-maai.
Kata 2, issoku-itto-no-maai.
Kata 3, issoku-itto-no-maai.
Kata 4, men is open.
Kata 5, men is open
Kata 6, shidachi is seme-ing kote-kote.
*Kata 7, I read shidachi is supposed to seme uchidachi's kote by lowing the kensen to kote, which forces uchidachi to do tsuki and men. However, I haven't seen any demonstration showing that.
Kata 8, shidachi is seme-ing kote.
Kata 9, shidachi is seme-ing mune-tsuki.
Kata 10, men is open.
I see a correlation here to shinsa.
Ikkyu needs to know kata 1 - 3: distance.
Shodan needs to know kata 1 - 5: distance + openings.
Nidan needs to know kata 1 - 7: distance + openings + seme.
Sandan and up needs to know kata 1-10: distance + openings + seme + kodachi.