I'm back on the computer where Tenhou works, and since I'm bored, I'll go over the game and I see if I agree with the other comments.
Your hand is all over the place because you are half-committing to the flush. For example, on the second go around when you draw 9p, you cut 3s even though it is less useful than 1m. This might make sense if you are going to boldly shoot for the flush; however, the very next draw is a 4s which you keep. Now the 4s is only useful if you can use it in a way that doesn't leave you furiten for the 3s. Later, you draw 5m and discard 8m, which changes your shape in that suit from a middle 6-8 wait to a double sided -56- wait, which is good. However, the very next turn, you draw a useless 1s, and discard 6m. Now you just have two isolated tiles (5m and 1s) that you can't use. If you weren't going to keep the 5m, then why didn't you discard when you drew it?
Late in the game, your hand looks like (dora: 9p):
and the player across from you cuts 9p. I would have called that and cut the East, as it would leave you tenpai for 1p and 8p. Of course, I say this only looking at your hand, cutting East would have actually dealt in to the player on your left. However, I'm not sure you could have guessed that.
I hate chanta/junchan, so I'm not sure I can comment unbiased here. I feel like you committed too early to junchan with your first call when the hand still had other possibilities. I also feel like you got rid of the dora too early. Regardless, calling the 4p ruined your hand, as it left you with no yaku. If you did it just to eat your opponent's ippatsu chance... I have no idea whether that's actually useful, but my guess would be no.
Okay. You got rid of the 1p too early when it could still connect with the 3p if you drew 2p. Fortunately you drew 4p later, meaning you didn't need the 1p after all.
Okay. I feel weird critiquing a hand that won, so I'll leave it at that.
As was mentioned before, dropping the 1m was a mistake. Even so, once it backfired and you drew 2m, you kept the 2m and then broke up the rest of your hand. The hand wasn't well suited to tanyao, because you have a complete 789s set, and the incomplete -23-m set has one side on a terminal (which you have already discarded). When you cut the 1m beside the 3m, you were basically giving up on 2m. Afterwards, you cut the potentially useful 3p instead of 2m. Worse, when you drew 6p, giving you the 6677p shape, you discard it. That shape is pretty useful, especially for this tanyao hand, as you can advance it with 5p, 6p, 7p, or 8p, and all of them are callable. Next, you draw 6m, which is also useful since it lets you call for a third 6m if necessary, but you discard it. You still have the 2m sitting in your hand, potentially leaving you furiten for 1m. When you call the red 5p, you discard 7p afterwards. This is fine with the hand that you had, but if you had not discarded 6p earlier, you would still have a good 67p shape in your hand. By the time you got your opponent's riichi, your hand was so messed up that you should have just defended.
As was already mentioned, you held back your hand by not calling 7p, and then you discarded them even though they were your likely pair.
Again, you kind of half-commit to the flush. I would have kept the possibility for using the 4m or 7s open, but I'll leave you to your decision to focus on the flush. However, you do this weird thing where you discard the 7s, and then bring the 6s into your hand. If you aren't going to use the 7s, then how are you planning to use the 6s? Thanks to that, you end up having the dangerous 6s still in your hand when your opponents declares riichi.
Nice. Choosing the 3m wait over the 2m, North wait isn't that big a deal.
It was unfortunate that you later drew 1s but couldn't add junchan since you were in riichi. However, I think the riichi was warranted.
Here it's just a matter of hand values. While I won't fault you for battling an opponent's riichi when you were looking at massive hands like some of those full-flushes; in this case the hand you're fighting for is just 1 han. You opponent's hand is certain to be worth more than yours, and is much closer to tenpai then yours. You should have defended.