Try use logical indexing. I am not familiar with ODE45 so there might be a nicer way to do this but in terms of plotting you could try this.

Code:

clear;clc;cla;
t0=0:0.01:2*pi;
t0=double(t0);
hold on
for x1=1:5
x0=[0,x1];
x0=double(x0);
[t,y]=ode45('test1',t0,x0);
t=double(t);
y=double(y);
Lind = (y(:,2) < 0 & t < pi);%use logical indexing
plot(y(Lind,1), y(Lind,2))
end
title('Gráfica general')
grid on
hold off
axis equal

The plot I get is only a quadrant tho so you might need to play with the code a bit. I did not fully understand your question so I hope that helps a bit.

Elbarto