The latest yearly Ichika event is out and it's based on the annual Kouhaku Uta Gassen event in Japan, where that year's most popular artists are divided into a red and white team and engage in a musical contest.
For this event, artists who have contributed to Bemani are divided into Team Red and Team Blue with a release schedule of 5 battles (pairs of songs), and the winning team gets to produce a bonus track that'll be added to games later.
The event will run from July 29 to September 30, with one battle a week for the first five weeks.
Essentially, play games to get cheer points (YELL). Unlocking a song is simply a matter of filling its gauge by sending YELL to it from this page, then (per usual) playing the games you want to unlock the song on at least once. Songs take 7200 points to unlock – I'll skip posting the full table of what game modes give how much YELL (see this table on the site for details).
Each song lists a main game and a number of support games (with the exception of the third week, where all games are essentially support games). Each game has its own YELL counter, and points from a game can only be used to contribute to unlocking the songs it's listed as either the main or support game for. The list of main/support games also determines which games the song is unlockable on.
This means that, for example, YELL points from SDVX/DDR/DRS/jubeat can go towards unlocking "ユメブキ", but not "DUAL STRIKER". This also means that "ユメブキ" can be played on SDVX/DDR/DRS/jubeat, but not "DUAL STRIKER".
The list of what games apply to which songs is available on the timetable page here.
Finally, if a game is the main game for a song, it gives a x5 bonus to the YELL provided. For example, for "ユメブキ" the main game is SDVX and for "DUAL STRIKER" it's IIDX. Since the third week has no main game, there is no bonus available.
The team with the most total YELL at the end of the event will get to produce a bonus track that'll be added to games at a later date. There is a counter on the front page of the event that shows the current totals for both teams.