The end was a bit fast. Talking about Ryouga and Rio instead of Rio and Kaito. But the rest of the story was great!

Aww...Cute. Though the thing I've noticed is that you use 'said' a lot. You should try using words like 'urged', 'exclaimed', 'retorted'. Have a variety.
Second, Kaito thinks before he decides on an action. You put: Kaito looked at his brother and nodded his head. You can add the word pondered in there. For example, Kaito looked at his brother, pondered for a second, and nodded his head.
Another thing I've been seeing. You seem to confuse the verb 'ask' and 'yell'. Here is your sentence: "So, you rather go talk to your friend than spend some time with me!" Rio asked.
Revised sentence: "So you'd rather go talk to your friend than spend some time with me?!" Rio asked angrily. Or something like that.
Well, overall, I liked it. It was cute. OCC on some parts, but things that can be overlooked. Oh yeah, you know when Kaito said, "Let's go Orbital", why didn't Orbital appear when they were feeding the ducks?

Aww, Ryoga, you're cute when you're overprotective. XD

In fact, this whole thing is so utterly adorable, I feel like I'm going to squee endlessly until I faint. Of course little Haruto is the one who says what everybody else is thinking. And the whole feeding-the-ducks situation is cute on its own.

I love that Ryoga apparently has enough duck-feeding expertise to know that there's more than one duck pond. It's so cute, and it really speaks to his relationship with his sister that he's willing to go feed ducks with her. And Kaito's consistent dodging of Haruto's questions is really cute, as well. Everyone's so in-character, and the prose is simple and crisp, which I like.

Overall, an adorable, fun little piece, and I enjoyed it very much! Good job! :)

Dawww This was really cute! XD

Maybe you should try adding in a few more choice 'moments' (which probably will make Ryoga rage if he ever caught them like that).

Good job I'm looking forward to more DiamondShipping fics from you

I LOVED IT! They may have not kissed but I still LOVED IT!:-)

Glad to hear. Sirius didn't.
Sirius: OF COURSE I DIDN'T!
Adorable oneshot, Galaxy-chan.
Sirius: She's ignoring me!

YAY! I love ducks! :DDD