Upcoming months no. Check the last week of events where they will tell you what ninja will be in the next month. Also, don't expect a ninja like jonin minato to sign-in. Expect a ninja that will be good for new players and awful for old players such as konohamaru teen.

Last year there was Anbu Itachi so I was hoping for a pretty good ninja like that

honestly, something like anbu itachi will probably never, if rarely ever, happen again. some time before that we had ninjas like gnw sakura (multiple times), gnw choji, hebihime, gnw sai. for a period of time, we also had sasuke + skillbooks, naruto + skillbooks, etc.

sign in ninjas will generally be very niche ninjas (ofc, nearly everything is good for new players lol cos they dont have a lot of choices), but never something meta. itachi anbu was a once-off occurrence and you shouldnt really get your hopes up.

The only reason why that happened is due to the other servers (China, Taiwan, Germany) getting him free as well. People would have complained if anbu itachi was not given for free since everyone knew about how he was given free. Before itachi, the sign-in ninjas were gnw ino, hinata, etc. type of ninjas, hebihime.

I'm pretty sure thats not the reason, because if thats the reason, then we should get some of pain from the login reward too. Chinese server gave pain gakido, chikushodo, etc for login reward. So nope, pretty sure thats not the reason.

None cared about pains because they are easily gainable by collection/instances/treasures for free.

A lot of people complained for months before 2017 xmas about itachi eventual availability for free (since he is not a free ninja), so, if he was not made available for free you would have had a riot.

For the pains none would have done it, but for itachi they would have.

They added pains in connection with their skill books/trials being added in the month of their sign-in. Knowing Oasis now, that's not going to happen.

In addition to that, Pain Fragments are always given as rewards for Arena Season Rewards, monthly ..

add to this: cn often gives ninja fragments and their skillbooks for sign in rewards if the breakthroughs were recently released. they've also given kinkaku/ginkaku/naruto ramen frags and skillbooks

we've had this a couple of times with team 7, but until oasis decides to seriously implement skillbooks/trials, we'll probably not get such rewards

Which brings back to my point about not expecting Oasis to give out the skillbook in sign-in, maybe in myoboku trial which won't be every time a new one comes out.