You will get this if you already have the Xbox 360 achievement
Your Rank is based on your Total Score (Overall Score + Overall Bonus Score), which is increased by playing Quick Match, Co-op Mode, Special Games and Skirmish Mode. You cannot increase your Overall Score past 50,000 (Rank 30) playing Skirmish Mode. You need a Total Score of 510,000 to reach Rank 50. You are halfway when you get to Rank 43. Happy Wars Wikia has a complete list of the Score required for each Rank
, together with the rewards.
The score you get from each match is the total of your Kill Score, Assist Score and Tactical Score. You can get additional bonus score from Premium Member Bonus (100%) and Boost Item Bonus (100%). A Premium Member 1 Day Pass costs 20 Happy Tickets, or you can buy a 7 Day Pass for 56 Happy Tickets or a 30 Day Pass for 180 Happy Tickets. You choose to use a Rank Up Boost at the end of each match. A Rank Up Boost costs 4 Happy Tickets, or you can buy 10 of them for 15 Happy Tickets. You can get Happy Tickets from completed Missions (eg Win a Quick Match battle for 5 Happy Tickets). Premium Member passes and Happy Tickets are sometimes given away. There are also special events that give bonus score.
A match can last up to 15 minutes, and the longer it lasts the better chance you have of increasing your Total Score. The more friends you have playing with you, the more you can control the match. You should be able to get a score of about 1,000 in a typical length match, and with both bonuses applied that would get you an additional bonus score of around 2,000. So whilst it will take around 140 hours to get an Overall Score of 510,000, you could reach Rank 50 in about 50 hours.
Your Overall Score (does not include Overall Bonus Score) is shown after every match, or you can check it from the mission The road to Score Hunter
found under Collections
-> Mission Mode